On 2/24/2025 7:38 PM, Adrian Hunter wrote:
On 20/02/25 12:50, Xiaoyao Li wrote:
On 1/29/2025 5:58 PM, Adrian Hunter wrote:
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Allow the use of kvm_load_host_xsave_state() with
vcpu->arch.guest_state_protected == true. This will allow TDX to reuse
kvm_load_host_xsave_state() instead of creating its own version.
For consistency, amend kvm_load_guest_xsave_state() also.
Ensure that guest state that kvm_load_host_xsave_state() depends upon,
such as MSR_IA32_XSS, cannot be changed by user space, if
guest_state_protected.
[Adrian: wrote commit message]
Link: https://lore.kernel.org/r/Z2GiQS_RmYeHU09L@xxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
TD vcpu enter/exit v2:
- New patch
---
arch/x86/kvm/svm/svm.c | 7 +++++--
arch/x86/kvm/x86.c | 18 +++++++++++-------
2 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7640a84e554a..b4bcfe15ad5e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4253,7 +4253,9 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
svm_set_dr6(svm, DR6_ACTIVE_LOW);
clgi();
- kvm_load_guest_xsave_state(vcpu);
+
+ if (!vcpu->arch.guest_state_protected)
+ kvm_load_guest_xsave_state(vcpu);
kvm_wait_lapic_expire(vcpu);
@@ -4282,7 +4284,8 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
- kvm_load_host_xsave_state(vcpu);
+ if (!vcpu->arch.guest_state_protected)
+ kvm_load_host_xsave_state(vcpu);
stgi();
/* Any pending NMI will happen here */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bbb6b7f40b3a..5cf9f023fd4b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1169,11 +1169,9 @@ EXPORT_SYMBOL_GPL(kvm_lmsw);
void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
{
- if (vcpu->arch.guest_state_protected)
- return;
+ WARN_ON_ONCE(vcpu->arch.guest_state_protected);
if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
-
if (vcpu->arch.xcr0 != kvm_host.xcr0)
xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
@@ -1192,13 +1190,11 @@ EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
{
- if (vcpu->arch.guest_state_protected)
- return;
-
if (cpu_feature_enabled(X86_FEATURE_PKU) &&
((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
- vcpu->arch.pkru = rdpkru();
+ if (!vcpu->arch.guest_state_protected)
+ vcpu->arch.pkru = rdpkru();
this needs justification.
It was proposed by Sean here:
https://lore.kernel.org/all/Z2WZ091z8GmGjSbC@xxxxxxxxxx/
which is part of the email thread referenced by the "Link:" tag above
IMHO, this change needs to be put in patch 07, which is the better place
to justify it.
if (vcpu->arch.pkru != vcpu->arch.host_pkru)
wrpkru(vcpu->arch.host_pkru);
}
@@ -3916,6 +3912,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
return 1;
+
+ if (vcpu->arch.guest_state_protected)
+ return 1;
+
this and below change need to be a separate patch. So that we can discuss independently.
I see no reason to make MSR_IA32_XSS special than other MSRs. When guest_state_protected, most of the MSRs that aren't emulated by KVM are inaccessible by KVM.
Yes, TDX will block access to MSR_IA32_XSS anyway because
tdx_has_emulated_msr() will return false for MSR_IA32_XSS.
However kvm_load_host_xsave_state() is not TDX-specific code and it
relies upon vcpu->arch.ia32_xss, so there is reason to block
access to it when vcpu->arch.guest_state_protected is true.
It is TDX specific logic that TDX requires vcpu->arch.ia32_xss unchanged
since TDX is going to utilize kvm_load_host_xsave_state() to restore
host xsave state and relies on vcpu->arch.ia32_xss to be always the
value of XFAM & XSS_MASK.
So please put this change into the TDX specific patch with the clear
justfication.
/*
* KVM supports exposing PT to the guest, but does not support
* IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than
@@ -4375,6 +4375,10 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
return 1;
+
+ if (vcpu->arch.guest_state_protected)
+ return 1;
+
msr_info->data = vcpu->arch.ia32_xss;
break;
case MSR_K7_CLK_CTL:
