Re: [PATCH v6 07/43] KVM: guest_memfd: Update kvm_gmem_populate() to use gmem attributes
From: Fuad Tabba
Date: Wed May 20 2026 - 09:48:38 EST
On Thu, 7 May 2026 at 21:22, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> Update the guest_memfd populate() flow to pull memory attributes from the
> gmem instance instead of the VM when KVM is not configured to track
> shared/private status in the VM.
>
> Rename the per-VM API to make it clear that it retrieves per-VM
> attributes, i.e. is not suitable for use outside of flows that are
> specific to generic per-VM attributes.
>
> Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
/fuad
> ---
> arch/x86/kvm/mmu/mmu.c | 2 +-
> include/linux/kvm_host.h | 14 +++++++++++++-
> virt/kvm/guest_memfd.c | 24 +++++++++++++++++++++---
> virt/kvm/kvm_main.c | 8 +++-----
> 4 files changed, 38 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 153bcc5369985..bfcf9be25598e 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -7997,7 +7997,7 @@ static bool hugepage_has_attrs(struct kvm *kvm, struct kvm_memory_slot *slot,
> const unsigned long end = start + KVM_PAGES_PER_HPAGE(level);
>
> if (level == PG_LEVEL_2M)
> - return kvm_range_has_memory_attributes(kvm, start, end, ~0, attrs);
> + return kvm_range_has_vm_memory_attributes(kvm, start, end, ~0, attrs);
>
> for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1)) {
> if (hugepage_test_mixed(slot, gfn, level - 1) ||
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 28a54298d27db..1deab76dc0a2c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2549,12 +2549,24 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> #endif
>
> #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
> -bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
> +extern bool vm_memory_attributes;
> +bool kvm_range_has_vm_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
> unsigned long mask, unsigned long attrs);
> bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
> struct kvm_gfn_range *range);
> bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
> struct kvm_gfn_range *range);
> +#else
> +#define vm_memory_attributes false
> +static inline bool kvm_range_has_vm_memory_attributes(struct kvm *kvm,
> + gfn_t start, gfn_t end,
> + unsigned long mask,
> + unsigned long attrs)
> +{
> + WARN_ONCE(1, "Unexpected call to kvm_range_has_vm_memory_attributes()");
> +
> + return false;
> +}
> #endif /* CONFIG_KVM_VM_MEMORY_ATTRIBUTES */
>
> unsigned long kvm_gmem_get_memory_attributes(struct kvm *kvm, gfn_t gfn);
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index f055e058a3f28..9d025f518c025 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -924,12 +924,31 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn);
>
> #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
> +static bool kvm_gmem_range_is_private(struct gmem_inode *gi, pgoff_t index,
> + size_t nr_pages, struct kvm *kvm, gfn_t gfn)
> +{
> + pgoff_t end = index + nr_pages - 1;
> + void *entry;
> +
> + if (vm_memory_attributes)
> + return kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + nr_pages,
> + KVM_MEMORY_ATTRIBUTE_PRIVATE,
> + KVM_MEMORY_ATTRIBUTE_PRIVATE);
> +
> + mt_for_each(&gi->attributes, entry, index, end) {
> + if (xa_to_value(entry) != KVM_MEMORY_ATTRIBUTE_PRIVATE)
> + return false;
> + }
> +
> + return true;
> +}
>
> static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot,
> struct file *file, gfn_t gfn, struct page *src_page,
> kvm_gmem_populate_cb post_populate, void *opaque)
> {
> pgoff_t index = kvm_gmem_get_index(slot, gfn);
> + struct gmem_inode *gi;
> struct folio *folio;
> kvm_pfn_t pfn;
> int ret;
> @@ -944,9 +963,8 @@ static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot,
>
> folio_unlock(folio);
>
> - if (!kvm_range_has_memory_attributes(kvm, gfn, gfn + 1,
> - KVM_MEMORY_ATTRIBUTE_PRIVATE,
> - KVM_MEMORY_ATTRIBUTE_PRIVATE)) {
> + gi = GMEM_I(file_inode(file));
> + if (!kvm_gmem_range_is_private(gi, index, 1, kvm, gfn)) {
> ret = -EINVAL;
> goto out_put_folio;
> }
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4139e903f756a..0a4024948711a 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -103,9 +103,7 @@ module_param(allow_unsafe_mappings, bool, 0444);
>
> #ifdef CONFIG_KVM_MEMORY_ATTRIBUTES
> #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
> -static bool vm_memory_attributes = true;
> -#else
> -#define vm_memory_attributes false
> +bool vm_memory_attributes = true;
> #endif
> DEFINE_STATIC_CALL_RET0(__kvm_get_memory_attributes, kvm_get_memory_attributes_t);
> EXPORT_SYMBOL_FOR_KVM_INTERNAL(STATIC_CALL_KEY(__kvm_get_memory_attributes));
> @@ -2450,7 +2448,7 @@ static unsigned long kvm_get_vm_memory_attributes(struct kvm *kvm, gfn_t gfn)
> * Returns true if _all_ gfns in the range [@start, @end) have attributes
> * such that the bits in @mask match @attrs.
> */
> -bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
> +bool kvm_range_has_vm_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
> unsigned long mask, unsigned long attrs)
> {
> XA_STATE(xas, &kvm->mem_attr_array, start);
> @@ -2584,7 +2582,7 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
> mutex_lock(&kvm->slots_lock);
>
> /* Nothing to do if the entire range has the desired attributes. */
> - if (kvm_range_has_memory_attributes(kvm, start, end, ~0, attributes))
> + if (kvm_range_has_vm_memory_attributes(kvm, start, end, ~0, attributes))
> goto out_unlock;
>
> /*
>
> --
> 2.54.0.563.g4f69b47b94-goog
>
>