On Tue, 18 Feb 2025 22:10:02 +1100
Alexey Kardashevskiy <aik@xxxxxxx> wrote:
> Currently private MMIO nested page faults are not expected so when
> such fault occurs, KVM tries moving the faulted page from private to
> shared which is not going to work as private MMIO is not backed by
> memfd.
>
> Handle private MMIO as shared: skip page state change and memfd
> page state tracking.
>
> The MMIO KVM memory slot is still marked as shared as the guest can
> access it as private or shared so marking the MMIO slot as private
> is not going to help.
>
> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxx>
> ---
> arch/x86/kvm/mmu/mmu.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 74c20dbb92da..32e27080b1c7 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4347,7 +4347,11 @@ static int __kvm_mmu_faultin_pfn(struct
> kvm_vcpu *vcpu, {
> unsigned int foll = fault->write ? FOLL_WRITE : 0;
>
> - if (fault->is_private)
> + if (fault->slot && fault->is_private &&
> !kvm_slot_can_be_private(fault->slot) &&
> + (vcpu->kvm->arch.vm_type == KVM_X86_SNP_VM))
> + pr_warn("%s: private SEV TIO MMIO fault for
> fault->gfn=%llx\n",
> + __func__, fault->gfn);
> + else if (fault->is_private)
> return kvm_mmu_faultin_pfn_private(vcpu, fault);
>
Let's fold this in a macro and make this more informative with comments.
> foll |= FOLL_NOWAIT;
