On 5/13/2025 10:04 PM, Fuad Tabba wrote:
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> This patch adds kvm_gmem_max_mapping_level(), which always returns
> PG_LEVEL_4K since guest_memfd only supports 4K pages for now.
>
> When guest_memfd supports shared memory, max_mapping_level (especially
> when recovering huge pages - see call to __kvm_mmu_max_mapping_level()
> from recover_huge_pages_range()) should take input from
> guest_memfd.
>
> Input from guest_memfd should be taken in these cases:
>
> + if the memslot supports shared memory (guest_memfd is used for
> shared memory, or in future both shared and private memory) or
> + if the memslot is only used for private memory and that gfn is
> private.
>
> If the memslot doesn't use guest_memfd, figure out the
> max_mapping_level using the host page tables like before.
>
> This patch also refactors and inlines the other call to
> __kvm_mmu_max_mapping_level().
>
> In kvm_mmu_hugepage_adjust(), guest_memfd's input is already
> provided (if applicable) in fault->max_level. Hence, there is no need
> to query guest_memfd.
>
> lpage_info is queried like before, and then if the fault is not from
> guest_memfd, adjust fault->req_level based on input from host page
> tables.
>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> ---
> arch/x86/kvm/mmu/mmu.c | 92 ++++++++++++++++++++++++++--------------
> include/linux/kvm_host.h | 7 +++
> virt/kvm/guest_memfd.c | 12 ++++++
> 3 files changed, 79 insertions(+), 32 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index cfbb471f7c70..9e0bc8114859 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3256,12 +3256,11 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
> return level;
> }
>
> -static int __kvm_mmu_max_mapping_level(struct kvm *kvm,
> - const struct kvm_memory_slot *slot,
> - gfn_t gfn, int max_level, bool is_private)
> +static int kvm_lpage_info_max_mapping_level(struct kvm *kvm,
> + const struct kvm_memory_slot *slot,
> + gfn_t gfn, int max_level)
> {
> struct kvm_lpage_info *linfo;
> - int host_level;
>
> max_level = min(max_level, max_huge_page_level);
> for ( ; max_level > PG_LEVEL_4K; max_level--) {
> @@ -3270,23 +3269,61 @@ static int __kvm_mmu_max_mapping_level(struct kvm *kvm,
> break;
> }
>
> - if (is_private)
> - return max_level;
> + return max_level;
> +}
> +
> +static inline u8 kvm_max_level_for_order(int order)
> +{
> + BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> +
> + KVM_MMU_WARN_ON(order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G) &&
> + order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M) &&
> + order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_4K));
> +
> + if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> + return PG_LEVEL_1G;
> +
> + if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> + return PG_LEVEL_2M;
> +
> + return PG_LEVEL_4K;
> +}
> +
> +static inline int kvm_gmem_max_mapping_level(const struct kvm_memory_slot *slot,
> + gfn_t gfn, int max_level)
> +{
> + int max_order;
>
> if (max_level == PG_LEVEL_4K)
> return PG_LEVEL_4K;
>
> - host_level = host_pfn_mapping_level(kvm, gfn, slot);
> - return min(host_level, max_level);
> + max_order = kvm_gmem_mapping_order(slot, gfn);
> + return min(max_level, kvm_max_level_for_order(max_order));
> }
>
> int kvm_mmu_max_mapping_level(struct kvm *kvm,
> const struct kvm_memory_slot *slot, gfn_t gfn)
> {
> - bool is_private = kvm_slot_has_gmem(slot) &&
> - kvm_mem_is_private(kvm, gfn);
> + int max_level;
> +
> + max_level = kvm_lpage_info_max_mapping_level(kvm, slot, gfn, PG_LEVEL_NUM);
> + if (max_level == PG_LEVEL_4K)
> + return PG_LEVEL_4K;
>
> - return __kvm_mmu_max_mapping_level(kvm, slot, gfn, PG_LEVEL_NUM, is_private);
> + if (kvm_slot_has_gmem(slot) &&
> + (kvm_gmem_memslot_supports_shared(slot) ||
> + kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE)) {
> + return kvm_gmem_max_mapping_level(slot, gfn, max_level);
> + }
> +
> + return min(max_level, host_pfn_mapping_level(kvm, gfn, slot));
> +}
> +
> +static inline bool fault_from_gmem(struct kvm_page_fault *fault)
> +{
> + return fault->is_private ||
> + (kvm_slot_has_gmem(fault->slot) &&
> + kvm_gmem_memslot_supports_shared(fault->slot));
> }
>
> void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> @@ -3309,12 +3346,20 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> * Enforce the iTLB multihit workaround after capturing the requested
> * level, which will be used to do precise, accurate accounting.
> */
> - fault->req_level = __kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> - fault->gfn, fault->max_level,
> - fault->is_private);
> + fault->req_level = kvm_lpage_info_max_mapping_level(vcpu->kvm, slot,
> + fault->gfn, fault->max_level);
> if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
> return;
>
> + if (!fault_from_gmem(fault)) {
> + int host_level;
> +
> + host_level = host_pfn_mapping_level(vcpu->kvm, fault->gfn, slot);
> + fault->req_level = min(fault->req_level, host_level);
> + if (fault->req_level == PG_LEVEL_4K)
> + return;
> + }
> +
> /*
> * mmu_invalidate_retry() was successful and mmu_lock is held, so
> * the pmd can't be split from under us.
> @@ -4448,23 +4493,6 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> vcpu->stat.pf_fixed++;
> }
>
> -static inline u8 kvm_max_level_for_order(int order)
> -{
> - BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> -
> - KVM_MMU_WARN_ON(order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G) &&
> - order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M) &&
> - order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_4K));
> -
> - if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> - return PG_LEVEL_1G;
> -
> - if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> - return PG_LEVEL_2M;
> -
> - return PG_LEVEL_4K;
> -}
> -
> static u8 kvm_max_level_for_fault_and_order(struct kvm *kvm,
> struct kvm_page_fault *fault,
> int order)
> @@ -4523,7 +4551,7 @@ static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcpu,
> {
> unsigned int foll = fault->write ? FOLL_WRITE : 0;
>
> - if (fault->is_private || kvm_gmem_memslot_supports_shared(fault->slot))
> + if (fault_from_gmem(fault))
> return kvm_mmu_faultin_pfn_gmem(vcpu, fault);
>
> foll |= FOLL_NOWAIT;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index de7b46ee1762..f9bb025327c3 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2560,6 +2560,7 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> gfn_t gfn, kvm_pfn_t *pfn, struct page **page,
> int *max_order);
> +int kvm_gmem_mapping_order(const struct kvm_memory_slot *slot, gfn_t gfn);
> #else
> static inline int kvm_gmem_get_pfn(struct kvm *kvm,
> struct kvm_memory_slot *slot, gfn_t gfn,
> @@ -2569,6 +2570,12 @@ static inline int kvm_gmem_get_pfn(struct kvm *kvm,
> KVM_BUG_ON(1, kvm);
> return -EIO;
> }
> +static inline int kvm_gmem_mapping_order(const struct kvm_memory_slot *slot,
> + gfn_t gfn)
> +{
> + BUG();
> + return 0;
> +}
> #endif /* CONFIG_KVM_GMEM */
>
> #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index fe0245335c96..b8e247063b20 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -774,6 +774,18 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> }
> EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
>
> +/**
> + * Returns the mapping order for this @gfn in @slot.
> + *
> + * This is equal to max_order that would be returned if kvm_gmem_get_pfn() were
> + * called now.
> + */
make W=1 ./ -s generates following warnings-
warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
* Returns the mapping order for this @gfn in @slot
This will fix it.
Subject: [PATCH] tmp
Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
virt/kvm/guest_memfd.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index b8e247063b20..d880b9098cc0 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -775,10 +775,12 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
/**
- * Returns the mapping order for this @gfn in @slot.
+ * kvm_gmem_mapping_order - Get the mapping order for a GFN.
+ * @slot: The KVM memory slot containing the @gfn.
+ * @gfn: The guest frame number to check.
*
- * This is equal to max_order that would be returned if kvm_gmem_get_pfn() were
- * called now.
+ * Returns: The mapping order for a @gfn in @slot. This is equal to max_order
+ * that kvm_gmem_get_pfn() would return for this @gfn.
*/
int kvm_gmem_mapping_order(const struct kvm_memory_slot *slot, gfn_t gfn)
{
--
2.34.1
Thanks,
Shivank
> +int kvm_gmem_mapping_order(const struct kvm_memory_slot *slot, gfn_t gfn)
> +{
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_gmem_mapping_order);
> +
> #ifdef CONFIG_KVM_GENERIC_GMEM_POPULATE
> long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long npages,
> kvm_gmem_populate_cb post_populate, void *opaque)
