Re: [PATCH v7 11/14] KVM: Register/unregister the guest private memory regions

From: Fuad Tabba
Date: Fri Aug 26 2022 - 11:26:09 EST

Hi Chao,

On Wed, Jul 6, 2022 at 9:27 AM Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
>
> If CONFIG_HAVE_KVM_PRIVATE_MEM=y, userspace can register/unregister the
> guest private memory regions through KVM_MEMORY_ENCRYPT_{UN,}REG_REGION
> ioctls. The patch reuses existing SEV ioctl but differs that the
> address in the region for private memory is gpa while SEV case it's hva.
>
> The private memory region is stored as xarray in KVM for memory
> efficiency in normal usages and zapping existing memory mappings is also
> a side effect of these two ioctls.
>
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
> Documentation/virt/kvm/api.rst | 17 +++++++---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/Kconfig | 1 +
> arch/x86/kvm/mmu.h | 2 --
> include/linux/kvm_host.h | 8 +++++
> virt/kvm/kvm_main.c | 57 +++++++++++++++++++++++++++++++++
> 6 files changed, 80 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 5ecfc7fbe0ee..dfb4caecab73 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -4715,10 +4715,19 @@ Documentation/virt/kvm/amd-memory-encryption.rst.
> This ioctl can be used to register a guest memory region which may
> contain encrypted data (e.g. guest RAM, SMRAM etc).
>
> -It is used in the SEV-enabled guest. When encryption is enabled, a guest
> -memory region may contain encrypted data. The SEV memory encryption
> -engine uses a tweak such that two identical plaintext pages, each at
> -different locations will have differing ciphertexts. So swapping or
> +Currently this ioctl supports registering memory regions for two usages:
> +private memory and SEV-encrypted memory.
> +
> +When private memory is enabled, this ioctl is used to register guest private
> +memory region and the addr/size of kvm_enc_region represents guest physical
> +address (GPA). In this usage, this ioctl zaps the existing guest memory
> +mappings in KVM that fallen into the region.
> +
> +When SEV-encrypted memory is enabled, this ioctl is used to register guest
> +memory region which may contain encrypted data for a SEV-enabled guest. The
> +addr/size of kvm_enc_region represents userspace address (HVA). The SEV
> +memory encryption engine uses a tweak such that two identical plaintext pages,
> +each at different locations will have differing ciphertexts. So swapping or
> moving ciphertext of those pages will not result in plaintext being
> swapped. So relocating (or migrating) physical backing pages for the SEV
> guest will require some additional steps.
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index dae190e19fce..92120e3a224e 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -37,6 +37,7 @@
> #include <asm/hyperv-tlfs.h>
>
> #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
> +#define __KVM_HAVE_ZAP_GFN_RANGE
>
> #define KVM_MAX_VCPUS 1024
>
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 1f160801e2a7..05861b9656a4 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -50,6 +50,7 @@ config KVM
> select HAVE_KVM_PM_NOTIFIER if PM
> select HAVE_KVM_PRIVATE_MEM if X86_64
> select MEMFILE_NOTIFIER if HAVE_KVM_PRIVATE_MEM
> + select XARRAY_MULTI if HAVE_KVM_PRIVATE_MEM
> help
> Support hosting fully virtualized guest machines using hardware
> virtualization extensions. You will need a fairly recent
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index a99acec925eb..428cd2e88cbd 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -209,8 +209,6 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> return -(u32)fault & errcode;
> }
>
> -void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end);
> -
> int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
>
> int kvm_mmu_post_init_vm(struct kvm *kvm);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 1b203c8aa696..da33f8828456 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -260,6 +260,10 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> #endif
>
> +#ifdef __KVM_HAVE_ZAP_GFN_RANGE
> +void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end);
> +#endif
> +
> enum {
> OUTSIDE_GUEST_MODE,
> IN_GUEST_MODE,
> @@ -795,6 +799,9 @@ struct kvm {
> struct notifier_block pm_notifier;
> #endif
> char stats_id[KVM_STATS_NAME_SIZE];
> +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> + struct xarray mem_attr_array;
> +#endif
> };
>
> #define kvm_err(fmt, ...) \
> @@ -1459,6 +1466,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> int kvm_arch_post_init_vm(struct kvm *kvm);
> void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> +bool kvm_arch_private_mem_supported(struct kvm *kvm);
>
> #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> /*
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 230c8ff9659c..bb714c2a4b06 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -914,6 +914,35 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
>
> #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
>
> +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> +#define KVM_MEM_ATTR_PRIVATE 0x0001
> +static int kvm_vm_ioctl_set_encrypted_region(struct kvm *kvm, unsigned int ioctl,
> + struct kvm_enc_region *region)
> +{
> + unsigned long start, end;
> + void *entry;
> + int r;
> +
> + if (region->size == 0 || region->addr + region->size < region->addr)
> + return -EINVAL;
> + if (region->addr & (PAGE_SIZE - 1) || region->size & (PAGE_SIZE - 1))
> + return -EINVAL;
> +
> + start = region->addr >> PAGE_SHIFT;
> + end = (region->addr + region->size - 1) >> PAGE_SHIFT;
> +
> + entry = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION ?
> + xa_mk_value(KVM_MEM_ATTR_PRIVATE) : NULL;
> +
> + r = xa_err(xa_store_range(&kvm->mem_attr_array, start, end,
> + entry, GFP_KERNEL_ACCOUNT));
> +
> + kvm_zap_gfn_range(kvm, start, end + 1);
> +
> + return r;
> +}
> +#endif /* CONFIG_HAVE_KVM_PRIVATE_MEM */
> +
> #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
> static int kvm_pm_notifier_call(struct notifier_block *bl,
> unsigned long state,
> @@ -1138,6 +1167,9 @@ static struct kvm *kvm_create_vm(unsigned long type)
> spin_lock_init(&kvm->mn_invalidate_lock);
> rcuwait_init(&kvm->mn_memslots_update_rcuwait);
> xa_init(&kvm->vcpu_array);
> +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> + xa_init(&kvm->mem_attr_array);
> +#endif
>
> INIT_LIST_HEAD(&kvm->gpc_list);
> spin_lock_init(&kvm->gpc_lock);
> @@ -1305,6 +1337,9 @@ 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_PRIVATE_MEM
> + xa_destroy(&kvm->mem_attr_array);
> +#endif
> cleanup_srcu_struct(&kvm->irq_srcu);
> cleanup_srcu_struct(&kvm->srcu);
> kvm_arch_free_vm(kvm);
> @@ -1508,6 +1543,11 @@ static void kvm_replace_memslot(struct kvm *kvm,
> }
> }
>
> +bool __weak kvm_arch_private_mem_supported(struct kvm *kvm)
> +{
> + return false;
> +}
> +
> static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> {
> u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> @@ -4689,6 +4729,22 @@ static long kvm_vm_ioctl(struct file *filp,
> r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> break;
> }
> +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> + case KVM_MEMORY_ENCRYPT_REG_REGION:
> + case KVM_MEMORY_ENCRYPT_UNREG_REGION: {
> + struct kvm_enc_region region;
> +
> + if (!kvm_arch_private_mem_supported(kvm))
> + goto arch_vm_ioctl;
> +
> + r = -EFAULT;
> + if (copy_from_user(&region, argp, sizeof(region)))
> + goto out;
> +
> + r = kvm_vm_ioctl_set_encrypted_region(kvm, ioctl, &region);
> + break;
> + }
> +#endif
> case KVM_GET_DIRTY_LOG: {
> struct kvm_dirty_log log;
>
> @@ -4842,6 +4898,7 @@ static long kvm_vm_ioctl(struct file *filp,
> r = kvm_vm_ioctl_get_stats_fd(kvm);
> break;
> default:
> +arch_vm_ioctl:

It might be good to make this label conditional on
CONFIG_HAVE_KVM_PRIVATE_MEM, otherwise you get a warning if
CONFIG_HAVE_KVM_PRIVATE_MEM isn't defined.

+#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
arch_vm_ioctl:
+#endif

Cheers,
/fuad





> r = kvm_arch_vm_ioctl(filp, ioctl, arg);
> }
> out:
> --
> 2.25.1
>