Messages in this thread | | | Date | Thu, 7 Mar 2024 11:49:11 +1300 | Subject | Re: [PATCH 11/16] KVM: x86/mmu: Explicitly disallow private accesses to emulated MMIO | From | "Huang, Kai" <> |
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On 7/03/2024 11:43 am, Sean Christopherson wrote: > On Thu, Mar 07, 2024, Kai Huang wrote: >> >> >> On 28/02/2024 3:41 pm, Sean Christopherson wrote: >>> Explicitly detect and disallow private accesses to emulated MMIO in >>> kvm_handle_noslot_fault() instead of relying on kvm_faultin_pfn_private() >>> to perform the check. This will allow the page fault path to go straight >>> to kvm_handle_noslot_fault() without bouncing through __kvm_faultin_pfn(). >>> >>> Signed-off-by: Sean Christopherson <seanjc@google.com> >>> --- >>> arch/x86/kvm/mmu/mmu.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c >>> index 5c8caab64ba2..ebdb3fcce3dc 100644 >>> --- a/arch/x86/kvm/mmu/mmu.c >>> +++ b/arch/x86/kvm/mmu/mmu.c >>> @@ -3314,6 +3314,11 @@ static int kvm_handle_noslot_fault(struct kvm_vcpu *vcpu, >>> { >>> gva_t gva = fault->is_tdp ? 0 : fault->addr; >>> + if (fault->is_private) { >>> + kvm_mmu_prepare_memory_fault_exit(vcpu, fault); >>> + return -EFAULT; >>> + } >>> + >> >> As mentioned in another reply in this series, unless I am mistaken, for TDX >> guest the _first_ MMIO access would still cause EPT violation with MMIO GFN >> being private. >> >> Returning to userspace cannot really help here because the MMIO mapping is >> inside the guest. > > That's a guest bug. The guest *knows* it's a TDX VM, it *has* to know. Accessing > emulated MMIO and thus taking a #VE before enabling paging is nonsensical. Either > enable paging and setup MMIO regions as shared, or go straight to TDCALL.
+Kirill,
I kinda forgot the detail, but what I am afraid is there might be bunch of existing TDX guests (since TDX guest code is upstream-ed) using unmodified drivers, which doesn't map MMIO regions as shared I suppose.
Kirill,
Could you clarify whether TDX guest code maps MMIO regions as shared since beginning?
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