Re: [PATCH kernel v7 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

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On Wed, Mar 08, 2017 at 02:00:11PM +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.
> 
> If we fail to update a hardware IOMMU table unexpected reason, we just
> clear it and move on as there is nothing really we can do about it -
> for example, if we hot plug a VFIO device to a guest, existing TCE tables
> will be mirrored automatically to the hardware and there is no interface
> to report to the guest about possible failures.
> 
> 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>

There are still a few oddities in the error paths.

[snip]
> +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;

IIR previous discussions properly, an xchg() failure should be a
WARN_ON().

[snip]
> +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 (WARN_ON_ONCE_RM(!pua))
> +		return H_HARDWARE;
> +
> +	pua = (void *) vmalloc_to_phys(pua);
> +	if (!pua)
> +		return H_TOO_HARD;

Here a vmalloc translation failure is treated as an 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;

Another xchg failure where I'd expect a WARN.

> +
> +	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;
> +}
> +
> +static long kvmppc_rm_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
> +		unsigned long entry, unsigned long ua,
> +		enum dma_data_direction dir)
> +{
> +	long ret;
> +	unsigned long hpa = 0;
> +	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;
> +
> +	mem = mm_iommu_lookup_rm(kvm->mm, ua, 1ULL << tbl->it_page_shift);
> +	if (!mem)
> +		return H_TOO_HARD;
> +
> +	if (WARN_ON_ONCE_RM(mm_iommu_ua_to_hpa_rm(mem, ua, &hpa)))
> +		return H_HARDWARE;
> +
> +	pua = (void *) vmalloc_to_phys(pua);
> +	if (WARN_ON_ONCE_RM(!pua))

.. but here a more or less identical vmalloc translation failure is
treated as a WARN.  Is it TOO_HARD, or WARN?

> +		return H_HARDWARE;
> +
> +	if (WARN_ON_ONCE_RM(mm_iommu_mapped_inc(mem)))
> +		return H_CLOSED;
> +
> +	ret = iommu_tce_xchg_rm(tbl, entry, &hpa, &dir);
> +	if (ret) {
> +		mm_iommu_mapped_dec(mem);
> +		return H_TOO_HARD;

And another xchg failure that I'd expect to be a warn

> +	}
> +
> +	if (dir != DMA_NONE)
> +		kvmppc_rm_tce_iommu_mapped_dec(kvm, tbl, entry);
> +
> +	*pua = ua;
> +
> +	return 0;
> +}
> +
>  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, ua = 0;
> +	enum dma_data_direction dir;
>  
>  	/* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
>  	/* 	    liobn, ioba, tce); */
> @@ -182,7 +304,32 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>  	if (ret != H_SUCCESS)
>  		return ret;
>  
> -	kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);
> +	dir = iommu_tce_direction(tce);
> +	if ((dir != DMA_NONE) && kvmppc_gpa_to_ua(vcpu->kvm,
> +			tce & ~(TCE_PCI_READ | TCE_PCI_WRITE), &ua, NULL))
> +		return H_PARAMETER;
> +
> +	entry = ioba >> stt->page_shift;
> +
> +	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->kvm,
> +					stit->tbl, entry, ua, dir);
> +
> +		if (ret == H_SUCCESS)
> +			continue;
> +
> +		if (ret == H_TOO_HARD)
> +			return ret;
> +
> +		WARN_ON_ONCE_RM(1);
> +		kvmppc_rm_clear_tce(stit->tbl, entry);
> +	}
> +
> +	kvmppc_tce_put(stt, entry, tce);
>  
>  	return H_SUCCESS;
>  }
> @@ -223,6 +370,7 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>  	unsigned long tces, entry, 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)
> @@ -293,6 +441,27 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>  		if (ret != H_SUCCESS)
>  			goto unlock_exit;
>  
> +		ua = 0;
> +		if (kvmppc_gpa_to_ua(vcpu->kvm,
> +				tce & ~(TCE_PCI_READ | TCE_PCI_WRITE),
> +				&ua, NULL))
> +			return H_PARAMETER;
> +
> +		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> +			ret = kvmppc_rm_tce_iommu_map(vcpu->kvm,
> +					stit->tbl, entry + i, ua,
> +					iommu_tce_direction(tce));
> +
> +			if (ret == H_SUCCESS)
> +				continue;
> +
> +			if (ret == H_TOO_HARD)
> +				goto unlock_exit;
> +
> +			WARN_ON_ONCE_RM(1);
> +			kvmppc_rm_clear_tce(stit->tbl, entry);
> +		}
> +
>  		kvmppc_tce_put(stt, entry + i, tce);
>  	}
>  
> @@ -309,6 +478,7 @@ 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)
> @@ -322,6 +492,24 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
>  	if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
>  		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 == H_SUCCESS)
> +				continue;
> +
> +			if (ret == H_TOO_HARD)
> +				return ret;
> +
> +			WARN_ON_ONCE_RM(1);
> +			kvmppc_rm_clear_tce(stit->tbl, entry);
> +		}
> +	}
> +
>  	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 95c91a9de351..62bdd6c48107 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -538,6 +538,8 @@ 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 */
> +	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);
> +
> +		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);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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