On Thu, Jul 17, 2025, Fuad Tabba wrote:
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> Update the KVM MMU fault handler to service guest page faults
> for memory slots backed by guest_memfd with mmap support. For such
> slots, the MMU must always fault in pages directly from guest_memfd,
> bypassing the host's userspace_addr.
>
> This ensures that guest_memfd-backed memory is always handled through
> the guest_memfd specific faulting path, regardless of whether it's for
> private or non-private (shared) use cases.
>
> Additionally, rename kvm_mmu_faultin_pfn_private() to
> kvm_mmu_faultin_pfn_gmem(), as this function is now used to fault in
> pages from guest_memfd for both private and non-private memory,
> accommodating the new use cases.
>
> Co-developed-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Co-developed-by: Fuad Tabba <tabba@xxxxxxxxxx>
> Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> ---
> arch/x86/kvm/mmu/mmu.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 94be15cde6da..ad5f337b496c 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4511,8 +4511,8 @@ static void kvm_mmu_finish_page_fault(struct kvm_vcpu *vcpu,
> r == RET_PF_RETRY, fault->map_writable);
> }
>
> -static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu,
> - struct kvm_page_fault *fault)
> +static int kvm_mmu_faultin_pfn_gmem(struct kvm_vcpu *vcpu,
> + struct kvm_page_fault *fault)
> {
> int max_order, r;
>
> @@ -4536,13 +4536,18 @@ static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu,
> return RET_PF_CONTINUE;
> }
>
> +static bool fault_from_gmem(struct kvm_page_fault *fault)
Drop the helper. It has exactly one caller, and it makes the code *harder* to
read, e.g. raises the question of what "from gmem" even means. If a separate
series follows and needs/justifies this helper, then it can/should be added then.
> +{
> + return fault->is_private || kvm_memslot_is_gmem_only(fault->slot);
> +}
> +
> static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcpu,
> struct kvm_page_fault *fault)
> {
> unsigned int foll = fault->write ? FOLL_WRITE : 0;
>
> - if (fault->is_private)
> - return kvm_mmu_faultin_pfn_private(vcpu, fault);
> + if (fault_from_gmem(fault))
> + return kvm_mmu_faultin_pfn_gmem(vcpu, fault);
>
> foll |= FOLL_NOWAIT;
> fault->pfn = __kvm_faultin_pfn(fault->slot, fault->gfn, foll,
> --
> 2.50.0.727.gbf7dc18ff4-goog
>
