On Tue, Jan 23, 2024 at 12:55 AM <isaku.yamahata@xxxxxxxxx> wrote:
>
> From: Chao Gao <chao.gao@xxxxxxxxx>
>
> Guest TD doesn't necessarily invoke MAP_GPA to convert the virtual MMIO
> range to shared before accessing it. When TD tries to access the virtual
> device's MMIO as shared, an EPT violation is raised first.
> kvm_mem_is_private() checks whether the GFN is shared or private. If
> MAP_GPA is not called for the GPA, KVM thinks the GPA is private and
> refuses shared access, and doesn't set up shared EPT entry. The guest
> can't make progress.
>
> Instead of requiring the guest to invoke MAP_GPA for regions of virtual
> MMIOs assume regions of virtual MMIOs are shared in KVM as well (i.e., GPAs
> either have no kvm_memory_slot or are backed by host MMIOs). So that guests
> can access those MMIO regions.
I'm not sure how the patch below deals with host MMIOs?
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
Missing Signed-off-by.
Also, this patch conflicts with "[PATCH v11 09/35] KVM: x86: Determine
shared/private faults based on vm_type". I think in general the logic
in that patch (which forces an exit to userspace if needed, to convert
the MMIO area to shared) can be applied to sw-protected and TDX guests
as well. I'm preparing a set of common patches that can be applied for
6.9 and will include something after testing with sw-protected VMs.
Paolo
> ---
> arch/x86/kvm/mmu/mmu.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e93bc16a5e9b..583ae9d6bf5d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4371,7 +4371,12 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> return RET_PF_EMULATE;
> }
>
> - if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
> + /*
> + * !fault->slot means MMIO. Don't require explicit GPA conversion for
> + * MMIO because MMIO is assigned at the boot time.
> + */
> + if (fault->slot &&
> + fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
> if (vcpu->kvm->arch.vm_type == KVM_X86_SW_PROTECTED_VM)
> return RET_PF_RETRY;
> kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
> --
> 2.25.1
>
