On 3/1/2025 3:34 PM, Paolo Bonzini wrote:
From: Yan Zhao <yan.y.zhao@xxxxxxxxx>
Always honor guest PAT in KVM-managed EPTs on TDX enabled platforms by
making self-snoop feature a hard dependency for TDX and making quirk
KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT not a valid quirk once TDX is enabled.
The quirk KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT only affects memory type of
KVM-managed EPTs. For the TDX-module-managed private EPT, memory type is
always forced to WB now.
Honoring guest PAT in KVM-managed EPTs ensures KVM does not invoke
kvm_zap_gfn_range() when attaching/detaching non-coherent DMA devices;
this would cause mirrored EPTs for TDs to be zapped, as well as incorrect
zapping of the private EPT that is managed by the TDX module.
As a new platform, TDX always comes with self-snoop feature supported and has
no worry to break old not-well-written yet unmodifiable guests. So, simply
force-disable the KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT quirk for TDX VMs.
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
Message-ID: <20250224071039.31511-1-yan.y.zhao@xxxxxxxxx>
[Use disabled_quirks instead of supported_quirks. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/vmx/tdx.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index b6f6f6e2f02e..4450fd99cb4c 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -624,6 +624,7 @@ int tdx_vm_init(struct kvm *kvm)
kvm->arch.has_protected_state = true;
kvm->arch.has_private_mem = true;
+ kvm->arch.disabled_quirks |= KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT;
This doesn't present userspace from dropping the
KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT bit by updating
kvm->arch.disabled_quirk via KVM_CAP_DISABLE_QUIRKS.
I think we can make inapplicable_quirks per VM in Patch 1 and set
kvm->arch.inapplicable_quirks |= KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT;
for TDX VMs.
/*
* Because guest TD is protected, VMM can't parse the instruction in TD.
@@ -3470,6 +3471,11 @@ int __init tdx_bringup(void)
goto success_disable_tdx;
}
+ if (!cpu_feature_enabled(X86_FEATURE_SELFSNOOP)) {
+ pr_err("Self-snoop is required for TDX\n");
+ goto success_disable_tdx;
+ }
+
if (!cpu_feature_enabled(X86_FEATURE_TDX_HOST_PLATFORM)) {
pr_err("tdx: no TDX private KeyIDs available\n");
goto success_disable_tdx;
