On Mon, 21 Jul 2025 at 17:47, Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> 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.
Ack.
Cheers,
/fuad
> > +{
> > + 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
> >
