Re: [PATCH kernel v4 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

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On 09/02/17 17:41, David Gibson wrote:
> On Tue, Feb 07, 2017 at 06:17:11PM +1100, Alexey Kardashevskiy wrote:
>> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
>> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
>> without passing them to user space which saves time on switching
>> to user space and back.
>>
>> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
>> KVM tries to handle a TCE request in the real mode, if failed
>> it passes the request to the virtual mode to complete the operation.
>> If it a virtual mode handler fails, the request is passed to
>> the user space; this is not expected to happen though.
>>
>> To avoid dealing with page use counters (which is tricky in real mode),
>> this only accelerates SPAPR TCE IOMMU v2 clients which are required
>> to pre-register the userspace memory. The very first TCE request will
>> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
>> of the TCE table (iommu_table::it_userspace) is not allocated till
>> the very first mapping happens and we cannot call vmalloc in real mode.
>>
>> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
>> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
>> and associates a physical IOMMU table with the SPAPR TCE table (which
>> is a guest view of the hardware IOMMU table). The iommu_table object
>> is cached and referenced so we do not have to look up for it in real mode.
>>
>> This does not implement the UNSET counterpart as there is no use for it -
>> once the acceleration is enabled, the existing userspace won't
>> disable it unless a VFIO container is destroyed; this adds necessary
>> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
>>
>> As this creates a descriptor per IOMMU table-LIOBN couple (called
>> kvmppc_spapr_tce_iommu_table), it is possible to have several
>> descriptors with the same iommu_table (hardware IOMMU table) attached
>> to the same LIOBN; we do not remove duplicates though as
>> iommu_table_ops::exchange not just update a TCE entry (which is
>> shared among IOMMU groups) but also invalidates the TCE cache
>> (one per IOMMU group).
>>
>> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
>> space.
>>
>> This finally makes use of vfio_external_user_iommu_id() which was
>> introduced quite some time ago and was considered for removal.
>>
>> Tests show that this patch increases transmission speed from 220MB/s
>> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
>> ---
>> Changes:
>> v4:
>> * added note to the commit log about allowing multiple updates of
>> the same IOMMU table;
>> * instead of checking for if any memory was preregistered, this
>> returns H_TOO_HARD if a specific page was not;
>> * fixed comments from v3 about error handling in many places;
>> * simplified TCE handlers and merged IOMMU parts inline - for example,
>> there used to be kvmppc_h_put_tce_iommu(), now it is merged into
>> kvmppc_h_put_tce(); this allows to check IOBA boundaries against
>> the first attached table only (makes the code simpler);
>>
>> v3:
>> * simplified not to use VFIO group notifiers
>> * reworked cleanup, should be cleaner/simpler now
>>
>> v2:
>> * reworked to use new VFIO notifiers
>> * now same iommu_table may appear in the list several times, to be fixed later
>> ---
>>
>> This has separate copies of handlers for real and virtual modes as
>> in fact H_PUT_TCE and H_STUFF_TCE could share a lot (common helpers
>> would take a "realmode" flag) but H_PUT_TCE_INDIRECT uses get_user()
>> in virtual mode and direct access in real mode and having a common
>> helper for it would make things uglier imho.
>>
>>
>> ---
>>  Documentation/virtual/kvm/devices/vfio.txt |  22 +-
>>  arch/powerpc/include/asm/kvm_host.h        |   8 +
>>  arch/powerpc/include/asm/kvm_ppc.h         |   4 +
>>  include/uapi/linux/kvm.h                   |   8 +
>>  arch/powerpc/kvm/book3s_64_vio.c           | 319 ++++++++++++++++++++++++++++-
>>  arch/powerpc/kvm/book3s_64_vio_hv.c        | 172 +++++++++++++++-
>>  arch/powerpc/kvm/powerpc.c                 |   2 +
>>  virt/kvm/vfio.c                            |  60 ++++++
>>  8 files changed, 590 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
>> index ef51740c67ca..f95d867168ea 100644
>> --- a/Documentation/virtual/kvm/devices/vfio.txt
>> +++ b/Documentation/virtual/kvm/devices/vfio.txt
>> @@ -16,7 +16,25 @@ Groups:
>>  
>>  KVM_DEV_VFIO_GROUP attributes:
>>    KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
>> +	kvm_device_attr.addr points to an int32_t file descriptor
>> +	for the VFIO group.
>>    KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking
>> +	kvm_device_attr.addr points to an int32_t file descriptor
>> +	for the VFIO group.
>> +  KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: attaches a guest visible TCE table
>> +	allocated by sPAPR KVM.
>> +	kvm_device_attr.addr points to a struct:
>>  
>> -For each, kvm_device_attr.addr points to an int32_t file descriptor
>> -for the VFIO group.
>> +	struct kvm_vfio_spapr_tce {
>> +		__u32	argsz;
>> +		__u32	flags;
>> +		__s32	groupfd;
>> +		__s32	tablefd;
>> +	};
>> +
>> +	where
>> +	@argsz is the size of kvm_vfio_spapr_tce_liobn;
>> +	@flags are not supported now, must be zero;
>> +	@groupfd is a file descriptor for a VFIO group;
>> +	@tablefd is a file descriptor for a TCE table allocated via
>> +		KVM_CREATE_SPAPR_TCE.
>> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
>> index e59b172666cd..a827006941f8 100644
>> --- a/arch/powerpc/include/asm/kvm_host.h
>> +++ b/arch/powerpc/include/asm/kvm_host.h
>> @@ -191,6 +191,13 @@ struct kvmppc_pginfo {
>>  	atomic_t refcnt;
>>  };
>>  
>> +struct kvmppc_spapr_tce_iommu_table {
>> +	struct rcu_head rcu;
>> +	struct list_head next;
>> +	struct vfio_group *group;
>> +	struct iommu_table *tbl;
>> +};
>> +
>>  struct kvmppc_spapr_tce_table {
>>  	struct list_head list;
>>  	struct kvm *kvm;
>> @@ -199,6 +206,7 @@ struct kvmppc_spapr_tce_table {
>>  	u32 page_shift;
>>  	u64 offset;		/* in pages */
>>  	u64 size;		/* window size in pages */
>> +	struct list_head iommu_tables;
>>  	struct page *pages[0];
>>  };
>>  
>> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
>> index 37bc9e7e90ba..da1410bd6b36 100644
>> --- a/arch/powerpc/include/asm/kvm_ppc.h
>> +++ b/arch/powerpc/include/asm/kvm_ppc.h
>> @@ -163,6 +163,10 @@ extern long kvmppc_prepare_vrma(struct kvm *kvm,
>>  extern void kvmppc_map_vrma(struct kvm_vcpu *vcpu,
>>  			struct kvm_memory_slot *memslot, unsigned long porder);
>>  extern int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu);
>> +extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
>> +		struct vfio_group *group);
>> +extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
>> +		struct vfio_group *group);
>>  
>>  extern long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>>  				struct kvm_create_spapr_tce_64 *args);
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index a2c9bb5a0ead..cdfa01169bd2 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1076,6 +1076,7 @@ struct kvm_device_attr {
>>  #define  KVM_DEV_VFIO_GROUP			1
>>  #define   KVM_DEV_VFIO_GROUP_ADD			1
>>  #define   KVM_DEV_VFIO_GROUP_DEL			2
>> +#define   KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE		3
>>  
>>  enum kvm_device_type {
>>  	KVM_DEV_TYPE_FSL_MPIC_20	= 1,
>> @@ -1097,6 +1098,13 @@ enum kvm_device_type {
>>  	KVM_DEV_TYPE_MAX,
>>  };
>>  
>> +struct kvm_vfio_spapr_tce {
>> +	__u32	argsz;
>> +	__u32	flags;
>> +	__s32	groupfd;
>> +	__s32	tablefd;
>> +};
>> +
>>  /*
>>   * ioctls for VM fds
>>   */
>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
>> index 9a7b7fca5e84..cb0469151e35 100644
>> --- a/arch/powerpc/kvm/book3s_64_vio.c
>> +++ b/arch/powerpc/kvm/book3s_64_vio.c
>> @@ -27,6 +27,10 @@
>>  #include <linux/hugetlb.h>
>>  #include <linux/list.h>
>>  #include <linux/anon_inodes.h>
>> +#include <linux/iommu.h>
>> +#include <linux/file.h>
>> +#include <linux/vfio.h>
>> +#include <linux/module.h>
>>  
>>  #include <asm/tlbflush.h>
>>  #include <asm/kvm_ppc.h>
>> @@ -39,6 +43,36 @@
>>  #include <asm/udbg.h>
>>  #include <asm/iommu.h>
>>  #include <asm/tce.h>
>> +#include <asm/mmu_context.h>
>> +
>> +static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
>> +{
>> +	void (*fn)(struct vfio_group *);
>> +
>> +	fn = symbol_get(vfio_group_put_external_user);
>> +	if (WARN_ON(!fn))
>> +		return;
>> +
>> +	fn(vfio_group);
>> +
>> +	symbol_put(vfio_group_put_external_user);
>> +}
>> +
>> +static int kvm_vfio_external_user_iommu_id(struct vfio_group *vfio_group)
>> +{
>> +	int (*fn)(struct vfio_group *);
>> +	int ret = -1;
>> +
>> +	fn = symbol_get(vfio_external_user_iommu_id);
>> +	if (!fn)
>> +		return ret;
>> +
>> +	ret = fn(vfio_group);
>> +
>> +	symbol_put(vfio_external_user_iommu_id);
>> +
>> +	return ret;
>> +}
>>  
>>  static unsigned long kvmppc_tce_pages(unsigned long iommu_pages)
>>  {
>> @@ -90,6 +124,123 @@ static long kvmppc_account_memlimit(unsigned long stt_pages, bool inc)
>>  	return ret;
>>  }
>>  
>> +static void kvm_spapr_tce_iommu_table_free(struct rcu_head *head)
>> +{
>> +	struct kvmppc_spapr_tce_iommu_table *stit = container_of(head,
>> +			struct kvmppc_spapr_tce_iommu_table, rcu);
>> +
>> +	iommu_table_put(stit->tbl);
>> +	kvm_vfio_group_put_external_user(stit->group);
>> +
>> +	kfree(stit);
>> +}
>> +
>> +static void kvm_spapr_tce_liobn_release_iommu_group(
>> +		struct kvmppc_spapr_tce_table *stt,
>> +		struct vfio_group *group)
>> +{
>> +	struct kvmppc_spapr_tce_iommu_table *stit, *tmp;
>> +
>> +	list_for_each_entry_safe(stit, tmp, &stt->iommu_tables, next) {
>> +		if (group && (stit->group != group))
>> +			continue;
>> +
>> +		list_del_rcu(&stit->next);
>> +
>> +		call_rcu(&stit->rcu, kvm_spapr_tce_iommu_table_free);
>> +	}
>> +}
>> +
>> +extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
>> +		struct vfio_group *group)
>> +{
>> +	struct kvmppc_spapr_tce_table *stt;
>> +
>> +	list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list)
>> +		kvm_spapr_tce_liobn_release_iommu_group(stt, group);
>> +}
>> +
>> +extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
>> +		struct vfio_group *group)
>> +{
>> +	struct kvmppc_spapr_tce_table *stt = NULL;
>> +	bool found = false;
>> +	struct iommu_table *tbl = NULL;
>> +	struct iommu_table_group *table_group;
>> +	long i, ret = 0;
>> +	struct kvmppc_spapr_tce_iommu_table *stit;
>> +	struct fd f;
>> +	int group_id;
>> +	struct iommu_group *grp;
>> +
>> +	group_id = kvm_vfio_external_user_iommu_id(group);
>> +	grp = iommu_group_get_by_id(group_id);
>> +	if (!grp)
>> +		return -EFAULT;
> 
> EFAULT doesn't look right, that's usually means userspace has give us
> a bad address.  What does failure to look up the iommu group by id
> mean here?


iommu_group_get_by_id() can fail -
1. if "something went very wrong" - as group ids are allocated when devices
are discovered so they are pretty static;
2. there is some racy sriov disable or host pci hotunplug;
3. kvm_vfio_external_user_iommu_id() returned invalid group id which means
that a device was unbound from the vfio-pci driver but the caller holds a
reference to vfio_group so this should not happen.


> 
>> +
>> +	f = fdget(tablefd);
>> +	if (!f.file) {
>> +		ret = -EBADF;
>> +		goto put_exit;
>> +	}
>> +
>> +	list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list) {
>> +		if (stt == f.file->private_data) {
>> +			found = true;
>> +			break;
>> +		}
>> +	}
>> +
>> +	fdput(f);
>> +
>> +	if (!found) {
>> +		ret = -ENODEV;
> 
> ENODEV doesn't look right either.  That generally means you're trying
> to use a device or facility that doesn't exist.  This case just means
> you've passed a file handle that either isn't a TCE table at all, or
> os one associated with a different VM.  -EINVAL, I guess, overloaded
> as it is.

Ok.



> 
>> +		goto put_exit;
> 
> Don't you need to put the table fd as well as the iommu group which
> you put in that exit path?


It is put few lines above.


>> +	}
>> +
>> +	table_group = iommu_group_get_iommudata(grp);
>> +	if (WARN_ON(!table_group)) {
>> +		ret = -EFAULT;
>> +		goto put_exit;
> 
> Again don't you need to put the table fd as well.

It is put few lines above, I do not keep it open longer than needed.


> 
>> +	}
>> +
>> +	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
>> +		struct iommu_table *tbltmp = table_group->tables[i];
>> +
>> +		if (!tbltmp)
>> +			continue;
>> +
>> +		/*
>> +		 * Make sure hardware table parameters are exactly the same;
>> +		 * this is used in the TCE handlers where boundary checks
>> +		 * use only the first attached table.
>> +		 */
>> +		if ((tbltmp->it_page_shift == stt->page_shift) &&
>> +				(tbltmp->it_offset == stt->offset) &&
>> +				(tbltmp->it_size == stt->size)) {
>> +			tbl = tbltmp;
>> +			break;
>> +		}
>> +	}
>> +	if (!tbl) {
>> +		ret = -ENODEV;
> 
> Again, ENODEV doesn't seem right.  Here the problem is that the host
> hardware constraints don't match the guest hardware constraints.
> Hmm.  EIO?  ENOSPC?


Neither is very appealing to me... EINVAL?
When I use "ENODEV", I am thinking of "there is no device with
expected/requested characteristics" but this is probably wrong.



> 
>> +		goto put_exit;
>> +	}
>> +
>> +	iommu_table_get(tbl);
>> +
>> +	stit = kzalloc(sizeof(*stit), GFP_KERNEL);
>> +	stit->tbl = tbl;
>> +	stit->group = group;
>> +
>> +	list_add_rcu(&stit->next, &stt->iommu_tables);
> 
> So if you add the same group to the same liobn multiple times, you'll
> get multiple identical entries in this list.
> 
> I guess that's mostly harmless... although.. does it allow the user to
> force the allocation of arbitrary amounts of kernel memory in that
> list?


Oh. No, I'll add a check to avoid duplicates, they do not make sense here.


> 
>> +put_exit:
>> +	iommu_group_put(grp);
>> +
>> +	return ret;
>> +}
>> +
>>  static void release_spapr_tce_table(struct rcu_head *head)
>>  {
>>  	struct kvmppc_spapr_tce_table *stt = container_of(head,
>> @@ -132,6 +283,8 @@ static int kvm_spapr_tce_release(struct inode *inode, struct file *filp)
>>  
>>  	list_del_rcu(&stt->list);
>>  
>> +	kvm_spapr_tce_liobn_release_iommu_group(stt, NULL /* release all */);
>> +
>>  	kvm_put_kvm(stt->kvm);
>>  
>>  	kvmppc_account_memlimit(
>> @@ -181,6 +334,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>>  	stt->offset = args->offset;
>>  	stt->size = size;
>>  	stt->kvm = kvm;
>> +	INIT_LIST_HEAD_RCU(&stt->iommu_tables);
>>  
>>  	for (i = 0; i < npages; i++) {
>>  		stt->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
>> @@ -209,11 +363,94 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>>  	return ret;
>>  }
>>  
>> +static long kvmppc_tce_iommu_mapped_dec(struct kvm *kvm,
>> +		struct iommu_table *tbl, unsigned long entry)
>> +{
>> +	struct mm_iommu_table_group_mem_t *mem = NULL;
>> +	const unsigned long pgsize = 1ULL << tbl->it_page_shift;
>> +	unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
>> +
>> +	if (!pua)
>> +		return H_HARDWARE;
> 
> What could trigger this error?  Should it be a WARN_ON?

Nothing should so yes, it can be WARN_ON.


> 
>> +	mem = mm_iommu_lookup(kvm->mm, *pua, pgsize);
>> +	if (!mem)
>> +		return H_TOO_HARD;
>> +
>> +	mm_iommu_mapped_dec(mem);
>> +
>> +	*pua = 0;
>> +
>> +	return H_SUCCESS;
>> +}
>> +
>> +static long kvmppc_tce_iommu_unmap(struct kvm *kvm,
>> +		struct iommu_table *tbl, unsigned long entry)
>> +{
>> +	enum dma_data_direction dir = DMA_NONE;
>> +	unsigned long hpa = 0;
>> +	long ret;
>> +
>> +	if (iommu_tce_xchg(tbl, entry, &hpa, &dir))
>> +		return H_HARDWARE;
>> +
>> +	if (dir == DMA_NONE)
>> +		return H_SUCCESS;
>> +
>> +	ret = kvmppc_tce_iommu_mapped_dec(kvm, tbl, entry);
>> +	if (ret != H_SUCCESS)
>> +		iommu_tce_xchg(tbl, entry, &hpa, &dir);
>> +
>> +	return ret;
>> +}
>> +
>> +long kvmppc_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
>> +		unsigned long entry, unsigned long gpa,
>> +		enum dma_data_direction dir)
>> +{
>> +	long ret;
>> +	unsigned long hpa, ua, *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
>> +	struct mm_iommu_table_group_mem_t *mem;
>> +
>> +	if (!pua)
>> +		/* it_userspace allocation might be delayed */
>> +		return H_TOO_HARD;
>> +
>> +	if (kvmppc_gpa_to_ua(kvm, gpa, &ua, NULL))
>> +		return H_PARAMETER;
>> +
>> +	mem = mm_iommu_lookup(kvm->mm, ua, 1ULL << tbl->it_page_shift);
>> +	if (!mem)
>> +		return H_TOO_HARD;
>> +
>> +	if (mm_iommu_ua_to_hpa(mem, ua, &hpa))
>> +		return H_HARDWARE;
> 
> IIUC this would happen if qemu had failed to preregister all of guest
> RAM, making this indeed an H_HARDWARE.


If QEMU failed to preregister, then mm_iommu_lookup() fails and it is
TOO_HARD. mm_iommu_ua_to_hpa() in this context cannot possibly fail (unless
broken memory) as it only returns error when out of bounds but
mm_iommu_lookup() ensures this.



> 
>> +	if (mm_iommu_mapped_inc(mem))
>> +		return H_HARDWARE;
> 
> I'm less clear on when this one would happen.


This may happen when there is a race with mm_iommu_put().


> 
>> +
>> +	ret = iommu_tce_xchg(tbl, entry, &hpa, &dir);
>> +	if (ret) {
>> +		mm_iommu_mapped_dec(mem);
>> +		return H_TOO_HARD;
>> +	}
>> +
>> +	if (dir != DMA_NONE)
>> +		kvmppc_tce_iommu_mapped_dec(kvm, tbl, entry);
>> +
>> +	*pua = ua;
>> +
>> +	return 0;
>> +}
>> +
>>  long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>>  		      unsigned long ioba, unsigned long tce)
>>  {
>>  	struct kvmppc_spapr_tce_table *stt;
>> -	long ret;
>> +	long ret, idx;
>> +	struct kvmppc_spapr_tce_iommu_table *stit;
>> +	unsigned long entry, gpa;
>> +	enum dma_data_direction dir;
>>  
>>  	/* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
>>  	/* 	    liobn, ioba, tce); */
>> @@ -230,6 +467,36 @@ long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>>  	if (ret != H_SUCCESS)
>>  		return ret;
>>  
>> +	stit = list_first_entry_or_null(&stt->iommu_tables,
>> +			struct kvmppc_spapr_tce_iommu_table, next);
>> +	if (stit) {
>> +		entry = ioba >> stit->tbl->it_page_shift;
>> +		gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +		dir = iommu_tce_direction(tce);
>> +
>> +		if (dir == DMA_NONE) {
>> +			if (iommu_tce_clear_param_check(stit->tbl, ioba, 0, 1))
>> +				return H_PARAMETER;
>> +		} else {
>> +			if (iommu_tce_put_param_check(stit->tbl, ioba, gpa))
> 
> Any way you could make these param check functions based on stt
> instead of stit->tbl?  That would let you do them before checking if
> there are any hw tables to update, avaoiding the somewhat awkward
> 	if (at least one)
> 		for (each one)
> construct.

I could:
1. change iommu_tce_put_param_check() to take shift, offset, size and drop
use of IOMMU_PAGE_MASK(tbl) (and change all callers in vfio_iommu_spapr_tce.c);
2. make a copy of iommu_tce_put_param_check() which would take stt.

And yet this code does operate with tbl anyway, akward either way imho...



> 
>> +				return H_PARAMETER;
>> +		}
>> +
>> +		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> +			if (dir == DMA_NONE) {
>> +				ret = kvmppc_tce_iommu_unmap(vcpu->kvm,
>> +						stit->tbl, entry);
>> +			} else {
>> +				idx = srcu_read_lock(&vcpu->kvm->srcu);
>> +				ret = kvmppc_tce_iommu_map(vcpu->kvm, stit->tbl,
>> +						entry, gpa, dir);
>> +				srcu_read_unlock(&vcpu->kvm->srcu, idx);
>> +			}
>> +			if (ret != H_SUCCESS)
>> +				return ret;
> 
> Doesn't this error path need to clean up for the case where you
> managed to update some backing TCE tables, but then failed later ones?

Probably.

This is what I asked in:
Re: [PATCH kernel v4 08/10] KVM: PPC: Separate TCE validation from update

Failure to update a hardware TCE table means we are in deep trouble, I
cannot think of any valid reason how we could get this far and not fail
before but fail now.


> 
>> +		}
>> +	}
>> +
>>  	kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);
>>  
>>  	return H_SUCCESS;
>> @@ -242,9 +509,10 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>  {
>>  	struct kvmppc_spapr_tce_table *stt;
>>  	long i, ret = H_SUCCESS, idx;
>> -	unsigned long entry, ua = 0;
>> +	unsigned long entry, gpa, ua = 0;
>>  	u64 __user *tces;
>>  	u64 tce;
>> +	struct kvmppc_spapr_tce_iommu_table *stit;
>>  
>>  	stt = kvmppc_find_table(vcpu->kvm, liobn);
>>  	if (!stt)
>> @@ -272,6 +540,9 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>  	}
>>  	tces = (u64 __user *) ua;
>>  
>> +	stit = list_first_entry_or_null(&stt->iommu_tables,
>> +			struct kvmppc_spapr_tce_iommu_table, next);
>> +
>>  	for (i = 0; i < npages; ++i) {
>>  		if (get_user(tce, tces + i)) {
>>  			ret = H_TOO_HARD;
>> @@ -282,6 +553,15 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>  		ret = kvmppc_tce_validate(stt, tce);
>>  		if (ret != H_SUCCESS)
>>  			goto unlock_exit;
>> +
>> +		if (stit) {
>> +			gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +			ret = iommu_tce_put_param_check(stit->tbl,
>> +					ioba + (i << stit->tbl->it_page_shift),
>> +					gpa);
>> +			if (ret != H_SUCCESS)
>> +				goto unlock_exit;
>> +		}
>>  	}
>>  
>>  	for (i = 0; i < npages; ++i) {
>> @@ -291,6 +571,21 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>  		}
>>  		tce = be64_to_cpu(tce);
>>  
>> +		if (stit) {
>> +			for (i = 0; i < npages; ++i) {
>> +				gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +
>> +				list_for_each_entry_lockless(stit,
>> +						&stt->iommu_tables, next) {
>> +					ret = kvmppc_tce_iommu_map(vcpu->kvm,
>> +						stit->tbl, entry + i, gpa,
>> +						iommu_tce_direction(tce));
>> +					if (ret != H_SUCCESS)
>> +						goto unlock_exit;
>> +				}
> 
> Um.. what value will this for_each leave in stit after completion?  I
> suspect it will be something bogus, which means re-using stit in the
> next 0..npages loop iteration won't be safe (you only initialize stit
> with the first entry outside that loop).


#define list_for_each_entry_lockless(pos, head, member) \
  for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \
     &pos->member != (head); \
     pos = list_entry_lockless(pos->member.next, typeof(*pos), member))

stit is "pos" which is reset every time the loop is called.


> 
>> +			}
>> +		}
>> +
>>  		kvmppc_tce_put(stt, entry + i, tce);
>>  	}
>>  
>> @@ -307,6 +602,7 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
>>  {
>>  	struct kvmppc_spapr_tce_table *stt;
>>  	long i, ret;
>> +	struct kvmppc_spapr_tce_iommu_table *stit;
>>  
>>  	stt = kvmppc_find_table(vcpu->kvm, liobn);
>>  	if (!stt)
>> @@ -320,6 +616,25 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
>>  	if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
>>  		return H_PARAMETER;
>>  
>> +	stit = list_first_entry_or_null(&stt->iommu_tables,
>> +			struct kvmppc_spapr_tce_iommu_table, next);
>> +	if (stit) {
>> +		if (iommu_tce_clear_param_check(stit->tbl, ioba,
>> +					tce_value, npages))
>> +			return H_PARAMETER;
>> +
>> +		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> +			unsigned long entry = ioba >> stit->tbl->it_page_shift;
>> +
>> +			for (i = 0; i < npages; ++i) {
>> +				ret = kvmppc_tce_iommu_unmap(vcpu->kvm,
>> +						stit->tbl, entry + i);
>> +				if (ret)
>> +					return ret;
> 
> Again do you need some sort of cleanup for partial completion?

Again,
Re: [PATCH kernel v4 08/10] KVM: PPC: Separate TCE validation from update

This is an unexpected failure which should not happen, what kind of cleanup
it would make sense to do here? Re-map what was mapped before H_STUFF_TCE
was called?


> 
> 
>> +			}
>> +		}
>> +	}
>> +
>>  	for (i = 0; i < npages; ++i, ioba += (1ULL << stt->page_shift))
>>  		kvmppc_tce_put(stt, ioba >> stt->page_shift, tce_value);
>>  
>> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
>> index dc1c66fda941..018c7d94a575 100644
>> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
>> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
>> @@ -178,11 +178,104 @@ long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long gpa,
>>  EXPORT_SYMBOL_GPL(kvmppc_gpa_to_ua);
>>  
>>  #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>> +static long kvmppc_rm_tce_iommu_mapped_dec(struct kvm *kvm,
>> +		struct iommu_table *tbl, unsigned long entry)
>> +{
>> +	struct mm_iommu_table_group_mem_t *mem = NULL;
>> +	const unsigned long pgsize = 1ULL << tbl->it_page_shift;
>> +	unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
>> +
>> +	if (!pua)
>> +		return H_HARDWARE;
>> +
>> +	pua = (void *) vmalloc_to_phys(pua);
>> +	if (!pua)
>> +		return H_TOO_HARD;
>> +
>> +	mem = mm_iommu_lookup_rm(kvm->mm, *pua, pgsize);
>> +	if (!mem)
>> +		return H_TOO_HARD;
>> +
>> +	mm_iommu_mapped_dec(mem);
>> +
>> +	*pua = 0;
>> +
>> +	return H_SUCCESS;
>> +}
>> +
>> +static long kvmppc_rm_tce_iommu_unmap(struct kvm *kvm,
>> +		struct iommu_table *tbl, unsigned long entry)
>> +{
>> +	enum dma_data_direction dir = DMA_NONE;
>> +	unsigned long hpa = 0;
>> +	long ret;
>> +
>> +	if (iommu_tce_xchg_rm(tbl, entry, &hpa, &dir))
>> +		return H_HARDWARE;
>> +
>> +	if (dir == DMA_NONE)
>> +		return H_SUCCESS;
>> +
>> +	ret = kvmppc_rm_tce_iommu_mapped_dec(kvm, tbl, entry);
>> +	if (ret)
>> +		iommu_tce_xchg_rm(tbl, entry, &hpa, &dir);
>> +
>> +	return ret;
>> +}
>> +
>> +long kvmppc_rm_tce_iommu_map(struct kvm_vcpu *vcpu, struct iommu_table *tbl,
>> +		unsigned long entry, unsigned long gpa,
>> +		enum dma_data_direction dir)
>> +{
>> +	long ret;
>> +	unsigned long hpa = 0, ua;
>> +	unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
>> +	struct mm_iommu_table_group_mem_t *mem;
>> +
>> +	if (!pua)
>> +		/* it_userspace allocation might be delayed */
>> +		return H_TOO_HARD;
>> +
>> +	if (kvmppc_gpa_to_ua(vcpu->kvm, gpa, &ua, NULL))
>> +		return H_PARAMETER;
>> +
>> +	mem = mm_iommu_lookup_rm(vcpu->kvm->mm, ua, 1ULL << tbl->it_page_shift);
>> +	if (!mem)
>> +		return H_TOO_HARD;
>> +
>> +	if (mm_iommu_ua_to_hpa_rm(mem, ua, &hpa))
>> +		return H_HARDWARE;
>> +
>> +	pua = (void *) vmalloc_to_phys(pua);
>> +	if (!pua)
>> +		return H_HARDWARE;
> 
> What circumstances can this fail under?  Does it need to be H_TOO_HARD instead?


When kernel memory gets corrupted and vmalloc_to_page() won't be able to
find a page which was allocated with vmalloc.


>> +
>> +	if (mm_iommu_mapped_inc(mem))
>> +		return H_HARDWARE;
>> +
>> +	ret = iommu_tce_xchg_rm(tbl, entry, &hpa, &dir);
>> +	if (ret) {
>> +		mm_iommu_mapped_dec(mem);
>> +		return H_TOO_HARD;
>> +	}
>> +
>> +	if (dir != DMA_NONE)
>> +		kvmppc_rm_tce_iommu_mapped_dec(vcpu->kvm, tbl, entry);
>> +
>> +	*pua = ua;
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(kvmppc_rm_tce_iommu_map);
>> +
>>  long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>>  		unsigned long ioba, unsigned long tce)
>>  {
>>  	struct kvmppc_spapr_tce_table *stt;
>>  	long ret;
>> +	struct kvmppc_spapr_tce_iommu_table *stit;
>> +	unsigned long entry, gpa;
>> +	enum dma_data_direction dir;
>>  
>>  	/* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
>>  	/* 	    liobn, ioba, tce); */
>> @@ -199,6 +292,33 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>>  	if (ret != H_SUCCESS)
>>  		return ret;
>>  
>> +	stit = list_first_entry_or_null(&stt->iommu_tables,
>> +			struct kvmppc_spapr_tce_iommu_table, next);
>> +	if (stit) {
>> +		entry = ioba >> stit->tbl->it_page_shift;
>> +		gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +		dir = iommu_tce_direction(tce);
>> +
>> +		if (dir == DMA_NONE) {
>> +			if (iommu_tce_clear_param_check(stit->tbl, ioba, 0, 1))
>> +				return H_PARAMETER;
>> +		} else {
>> +			if (iommu_tce_put_param_check(stit->tbl, ioba, gpa))
>> +				return H_PARAMETER;
>> +		}
>> +
>> +		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> +			if (dir == DMA_NONE)
>> +				ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm,
>> +						stit->tbl, entry);
>> +			else
>> +				ret = kvmppc_rm_tce_iommu_map(vcpu, stit->tbl,
>> +						entry, gpa, dir);
>> +			if (ret != H_SUCCESS)
>> +				return ret;
>> +		}
>> +	}
>> +
>>  	kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);
>>  
>>  	return H_SUCCESS;
>> @@ -237,9 +357,10 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>  {
>>  	struct kvmppc_spapr_tce_table *stt;
>>  	long i, ret = H_SUCCESS;
>> -	unsigned long tces, entry, tce, ua = 0;
>> +	unsigned long tces, entry, gpa, tce, ua = 0;
>>  	unsigned long *rmap = NULL;
>>  	bool prereg = false;
>> +	struct kvmppc_spapr_tce_iommu_table *stit;
>>  
>>  	stt = kvmppc_find_table(vcpu->kvm, liobn);
>>  	if (!stt)
>> @@ -303,17 +424,45 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>  		}
>>  	}
>>  
>> +	stit = list_first_entry_or_null(&stt->iommu_tables,
>> +			struct kvmppc_spapr_tce_iommu_table, next);
>> +
>>  	for (i = 0; i < npages; ++i) {
>>  		tce = be64_to_cpu(((u64 *)tces)[i]);
>>  
>>  		ret = kvmppc_tce_validate(stt, tce);
>>  		if (ret != H_SUCCESS)
>>  			goto unlock_exit;
>> +
>> +		if (stit) {
>> +			gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +			ret = iommu_tce_put_param_check(stit->tbl,
>> +					ioba + (i << stit->tbl->it_page_shift),
>> +					gpa);
>> +			if (ret != H_SUCCESS)
>> +				goto unlock_exit;
>> +
>> +		}
>>  	}
>>  
>>  	for (i = 0; i < npages; ++i) {
>>  		tce = be64_to_cpu(((u64 *)tces)[i]);
> 
> As noted in the earlier patch this is really dangerous - by reloading
> the tce from userspace you've thrown away the verification above.


Sure, I am adding a tces cache to kvm_vcpu.


>> +		if (stit) {
>> +			for (i = 0; i < npages; ++i) {
>> +				gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +
>> +				list_for_each_entry_lockless(stit,
>> +						&stt->iommu_tables, next) {
>> +					ret = kvmppc_rm_tce_iommu_map(vcpu,
>> +						stit->tbl, entry + i, gpa,
>> +						iommu_tce_direction(tce));
>> +					if (ret != H_SUCCESS)
>> +						goto unlock_exit;
>> +				}
>> +			}
>> +		}
>> +
>>  		kvmppc_tce_put(stt, entry + i, tce);
>>  	}
>>  
>> @@ -330,6 +479,8 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
>>  {
>>  	struct kvmppc_spapr_tce_table *stt;
>>  	long i, ret;
>> +	struct kvmppc_spapr_tce_iommu_table *stit;
>> +
>>  
>>  	stt = kvmppc_find_table(vcpu->kvm, liobn);
>>  	if (!stt)
>> @@ -343,6 +494,25 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
>>  	if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
>>  		return H_PARAMETER;
>>  
>> +	stit = list_first_entry_or_null(&stt->iommu_tables,
>> +			struct kvmppc_spapr_tce_iommu_table, next);
>> +	if (stit) {
>> +		if (iommu_tce_clear_param_check(stit->tbl, ioba,
>> +					tce_value, npages))
>> +			return H_PARAMETER;
>> +
>> +		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> +			unsigned long entry = ioba >> stit->tbl->it_page_shift;
>> +
>> +			for (i = 0; i < npages; ++i) {
>> +				ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm,
>> +						stit->tbl, entry + i);
>> +				if (ret)
>> +					return ret;
>> +			}
>> +		}
>> +	}
>> +
>>  	for (i = 0; i < npages; ++i, ioba += (1ULL << stt->page_shift))
>>  		kvmppc_tce_put(stt, ioba >> stt->page_shift, tce_value);
>>  
>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>> index cd892dec7cb6..f3127dc87912 100644
>> --- a/arch/powerpc/kvm/powerpc.c
>> +++ b/arch/powerpc/kvm/powerpc.c
>> @@ -536,6 +536,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  #ifdef CONFIG_PPC_BOOK3S_64
>>  	case KVM_CAP_SPAPR_TCE:
>>  	case KVM_CAP_SPAPR_TCE_64:
>> +		/* fallthrough */
> 
> I'm not sure why this one should get a fallthrough comment, when none
> of the other cases do.


I believe it was either ignored then or checkpatch.pl did not warn about
this at the time.


> 
>> +	case KVM_CAP_SPAPR_TCE_VFIO:
>>  	case KVM_CAP_PPC_RTAS:
>>  	case KVM_CAP_PPC_FIXUP_HCALL:
>>  	case KVM_CAP_PPC_ENABLE_HCALL:
>> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
>> index d32f239eb471..2b7dc22265fe 100644
>> --- a/virt/kvm/vfio.c
>> +++ b/virt/kvm/vfio.c
>> @@ -20,6 +20,10 @@
>>  #include <linux/vfio.h>
>>  #include "vfio.h"
>>  
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> +#include <asm/kvm_ppc.h>
>> +#endif
>> +
>>  struct kvm_vfio_group {
>>  	struct list_head node;
>>  	struct vfio_group *vfio_group;
>> @@ -211,6 +215,9 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>  
>>  		mutex_unlock(&kv->lock);
>>  
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> +		kvm_spapr_tce_release_iommu_group(dev->kvm, vfio_group);
>> +#endif
>>  		kvm_vfio_group_set_kvm(vfio_group, NULL);
>>  
>>  		kvm_vfio_group_put_external_user(vfio_group);
>> @@ -218,6 +225,53 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>  		kvm_vfio_update_coherency(dev);
>>  
>>  		return ret;
>> +
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> +	case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: {
>> +		struct kvm_vfio_spapr_tce param;
>> +		unsigned long minsz;
>> +		struct kvm_vfio *kv = dev->private;
>> +		struct vfio_group *vfio_group;
>> +		struct kvm_vfio_group *kvg;
>> +		struct fd f;
>> +
>> +		minsz = offsetofend(struct kvm_vfio_spapr_tce, tablefd);
>> +
>> +		if (copy_from_user(&param, (void __user *)arg, minsz))
>> +			return -EFAULT;
>> +
>> +		if (param.argsz < minsz || param.flags)
>> +			return -EINVAL;
>> +
>> +		f = fdget(param.groupfd);
>> +		if (!f.file)
>> +			return -EBADF;
>> +
>> +		vfio_group = kvm_vfio_group_get_external_user(f.file);
>> +		fdput(f);
>> +
>> +		if (IS_ERR(vfio_group))
>> +			return PTR_ERR(vfio_group);
>> +
> 
> 
> Is there any particular reason you unwrap the group fd here, but the
> table fd inside kvm__spapr_tce_attach_iommu_group()?

No particular reason, just an intention not to spread too much spapr to KVM
VFIO device and vfio_group to POWER KVM.

I only unwrapp table_fd to see if it is in the kvm->arch.spapr_tce_tables
list, I am trying to keep spapr_tce_tables and kvmppc_spapr_tce_iommu_table
local to arch/powerpc/kvm/book3s_64_vio*.c

Unwrapping groupfd in arch/powerpc/kvm/book3s_64_vio*.c would mean
duplicating all kvm_vfio_group_get_external_user()/etc stubs in
arch/powerpc/kvm/book3s_64_vio.c, I did not want to duplicate these stubs.
I could but since I already have vfio_group unwrapped here, it seems
pointless to unwrap it over again in arch/powerpc/kvm/book3s_64_vio.c,
should I?



> 
>> +		ret = -ENOENT;
>> +
>> +		mutex_lock(&kv->lock);
>> +
>> +		list_for_each_entry(kvg, &kv->group_list, node) {
>> +			if (kvg->vfio_group != vfio_group)
>> +				continue;
>> +
>> +			ret = kvm_spapr_tce_attach_iommu_group(dev->kvm,
>> +					param.tablefd, vfio_group);
>> +
>> +			break;
>> +		}
>> +
>> +		mutex_unlock(&kv->lock);
>> +
>> +		return ret;
>> +	}
>> +#endif /* CONFIG_SPAPR_TCE_IOMMU */
>>  	}
>>  
>>  	return -ENXIO;
>> @@ -242,6 +296,9 @@ static int kvm_vfio_has_attr(struct kvm_device *dev,
>>  		switch (attr->attr) {
>>  		case KVM_DEV_VFIO_GROUP_ADD:
>>  		case KVM_DEV_VFIO_GROUP_DEL:
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> +		case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE:
>> +#endif
>>  			return 0;
>>  		}
>>  
>> @@ -257,6 +314,9 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
>>  	struct kvm_vfio_group *kvg, *tmp;
>>  
>>  	list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> +		kvm_spapr_tce_release_iommu_group(dev->kvm, kvg->vfio_group);
>> +#endif
>>  		kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
>>  		kvm_vfio_group_put_external_user(kvg->vfio_group);
>>  		list_del(&kvg->node);
> 


-- 
Alexey

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