On 12/2/2022 2:13 PM, Chao Peng wrote: > In confidential computing usages, whether a page is private or shared is > necessary information for KVM to perform operations like page fault > handling, page zapping etc. There are other potential use cases for > per-page memory attributes, e.g. to make memory read-only (or no-exec, > or exec-only, etc.) without having to modify memslots. > > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow > userspace to operate on the per-page memory attributes. > - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to > a guest memory range. > - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported > memory attributes. > > KVM internally uses xarray to store the per-page memory attributes. > > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@xxxxxxxxxx/ > --- > Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++ > arch/x86/kvm/Kconfig | 1 + > include/linux/kvm_host.h | 3 ++ > include/uapi/linux/kvm.h | 17 ++++++++ > virt/kvm/Kconfig | 3 ++ > virt/kvm/kvm_main.c | 76 ++++++++++++++++++++++++++++++++++ > 6 files changed, 163 insertions(+) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 5617bc4f899f..bb2f709c0900 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct. > The "pad" and "reserved" fields may be used for future extensions and should be > set to 0s by userspace. > > +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES > +----------------------------------------- > + > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES > +:Architectures: x86 > +:Type: vm ioctl > +:Parameters: u64 memory attributes bitmask(out) > +:Returns: 0 on success, <0 on error > + > +Returns supported memory attributes bitmask. Supported memory attributes will > +have the corresponding bits set in u64 memory attributes bitmask. > + > +The following memory attributes are defined:: > + > + #define KVM_MEMORY_ATTRIBUTE_READ (1ULL << 0) > + #define KVM_MEMORY_ATTRIBUTE_WRITE (1ULL << 1) > + #define KVM_MEMORY_ATTRIBUTE_EXECUTE (1ULL << 2) > + #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3) > + > +4.139 KVM_SET_MEMORY_ATTRIBUTES > +----------------------------------------- > + > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES > +:Architectures: x86 > +:Type: vm ioctl > +:Parameters: struct kvm_memory_attributes(in/out) > +:Returns: 0 on success, <0 on error > + > +Sets memory attributes for pages in a guest memory range. Parameters are > +specified via the following structure:: > + > + struct kvm_memory_attributes { > + __u64 address; > + __u64 size; > + __u64 attributes; > + __u64 flags; > + }; > + > +The user sets the per-page memory attributes to a guest memory range indicated > +by address/size, and in return KVM adjusts address and size to reflect the > +actual pages of the memory range have been successfully set to the attributes. > +If the call returns 0, "address" is updated to the last successful address + 1 > +and "size" is updated to the remaining address size that has not been set > +successfully. The user should check the return value as well as the size to > +decide if the operation succeeded for the whole range or not. The user may want > +to retry the operation with the returned address/size if the previous range was > +partially successful. > + > +Both address and size should be page aligned and the supported attributes can be > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES. > + > +The "flags" field may be used for future extensions and should be set to 0s. > + > 5. The kvm_run structure > ======================== > > @@ -8270,6 +8323,16 @@ structure. > When getting the Modified Change Topology Report value, the attr->addr > must point to a byte where the value will be stored or retrieved from. > > +8.40 KVM_CAP_MEMORY_ATTRIBUTES > +------------------------------ > + > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES > +:Architectures: x86 > +:Type: vm > + > +This capability indicates KVM supports per-page memory attributes and ioctls > +KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available. > + > 9. Known KVM API problems > ========================= > > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig > index fbeaa9ddef59..a8e379a3afee 100644 > --- a/arch/x86/kvm/Kconfig > +++ b/arch/x86/kvm/Kconfig > @@ -49,6 +49,7 @@ config KVM > select SRCU > select INTERVAL_TREE > select HAVE_KVM_PM_NOTIFIER if PM > + select HAVE_KVM_MEMORY_ATTRIBUTES > help > Support hosting fully virtualized guest machines using hardware > virtualization extensions. You will need a fairly recent > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 8f874a964313..a784e2b06625 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -800,6 +800,9 @@ struct kvm { > > #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER > struct notifier_block pm_notifier; > +#endif > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES > + struct xarray mem_attr_array; > #endif > char stats_id[KVM_STATS_NAME_SIZE]; > }; > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 64dfe9c07c87..5d0941acb5bb 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -1182,6 +1182,7 @@ struct kvm_ppc_resize_hpt { > #define KVM_CAP_S390_CPU_TOPOLOGY 222 > #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223 > #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224 > +#define KVM_CAP_MEMORY_ATTRIBUTES 225 > > #ifdef KVM_CAP_IRQ_ROUTING > > @@ -2238,4 +2239,20 @@ struct kvm_s390_zpci_op { > /* flags for kvm_s390_zpci_op->u.reg_aen.flags */ > #define KVM_S390_ZPCIOP_REGAEN_HOST (1 << 0) > > +/* Available with KVM_CAP_MEMORY_ATTRIBUTES */ > +#define KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES _IOR(KVMIO, 0xd2, __u64) > +#define KVM_SET_MEMORY_ATTRIBUTES _IOWR(KVMIO, 0xd3, struct kvm_memory_attributes) > + > +struct kvm_memory_attributes { > + __u64 address; > + __u64 size; > + __u64 attributes; > + __u64 flags; > +}; > + > +#define KVM_MEMORY_ATTRIBUTE_READ (1ULL << 0) > +#define KVM_MEMORY_ATTRIBUTE_WRITE (1ULL << 1) > +#define KVM_MEMORY_ATTRIBUTE_EXECUTE (1ULL << 2) > +#define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3) > + > #endif /* __LINUX_KVM_H */ > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig > index 800f9470e36b..effdea5dd4f0 100644 > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -19,6 +19,9 @@ config HAVE_KVM_IRQ_ROUTING > config HAVE_KVM_DIRTY_RING > bool > > +config HAVE_KVM_MEMORY_ATTRIBUTES > + bool > + > # Only strongly ordered architectures can select this, as it doesn't > # put any explicit constraint on userspace ordering. They can also > # select the _ACQ_REL version. > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 1782c4555d94..7f0f5e9f2406 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) > spin_lock_init(&kvm->mn_invalidate_lock); > rcuwait_init(&kvm->mn_memslots_update_rcuwait); > xa_init(&kvm->vcpu_array); > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES > + xa_init(&kvm->mem_attr_array); > +#endif > > INIT_LIST_HEAD(&kvm->gpc_list); > spin_lock_init(&kvm->gpc_lock); > @@ -1323,6 +1326,9 @@ static void kvm_destroy_vm(struct kvm *kvm) > kvm_free_memslots(kvm, &kvm->__memslots[i][0]); > kvm_free_memslots(kvm, &kvm->__memslots[i][1]); > } > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES > + xa_destroy(&kvm->mem_attr_array); > +#endif > cleanup_srcu_struct(&kvm->irq_srcu); > cleanup_srcu_struct(&kvm->srcu); > kvm_arch_free_vm(kvm); > @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm, > } > #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */ > > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES > +static u64 kvm_supported_mem_attributes(struct kvm *kvm) > +{ > + return 0; > +} > + > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm, > + struct kvm_memory_attributes *attrs) > +{ > + gfn_t start, end; > + unsigned long i; > + void *entry; > + u64 supported_attrs = kvm_supported_mem_attributes(kvm); > + > + /* flags is currently not used. */ > + if (attrs->flags) > + return -EINVAL; > + if (attrs->attributes & ~supported_attrs) > + return -EINVAL; > + if (attrs->size == 0 || attrs->address + attrs->size < attrs->address) > + return -EINVAL; > + if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size)) > + return -EINVAL; > + > + start = attrs->address >> PAGE_SHIFT; > + end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT; > + > + entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL; > + Because guest memory defaults to private, and now this patch stores the attributes with KVM_MEMORY_ATTRIBUTE_PRIVATE instead of _SHARED, it would bring more KVM_EXIT_MEMORY_FAULT exits at the beginning of boot time. Maybe it can be optimized somehow in other places? e.g. set mem attr in advance. > + mutex_lock(&kvm->lock); > + for (i = start; i < end; i++) > + if (xa_err(xa_store(&kvm->mem_attr_array, i, entry, > + GFP_KERNEL_ACCOUNT))) > + break; > + mutex_unlock(&kvm->lock); > + > + attrs->address = i << PAGE_SHIFT; > + attrs->size = (end - i) << PAGE_SHIFT; > + > + return 0; > +} > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */ > + > struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn) > { > return __gfn_to_memslot(kvm_memslots(kvm), gfn);
