On 12/5/23 17:49, Michael Roth wrote:
In general, activating long mode involves setting the EFER_LME bit in
the EFER register and then enabling the X86_CR0_PG bit in the CR0
register. At this point, the EFER_LMA bit will be set automatically by
hardware.
In the case of SVM/SEV guests where writes to CR0 are intercepted, it's
necessary for the host to set EFER_LMA on behalf of the guest since
hardware does not see the actual CR0 write.
In the case of SEV-ES guests where writes to CR0 are trapped instead of
intercepted, the hardware *does* see/record the write to CR0 before
exiting and passing the value on to the host, so as part of enabling
SEV-ES support commit f1c6366e3043 ("KVM: SVM: Add required changes to
support intercepts under SEV-ES") dropped special handling of the
EFER_LMA bit with the understanding that it would be set automatically.
Maybe add here that it was thought that the change to EFER would generate
a trap. However, a trap isn't generated for hardware changes to EFER and
only explicit writes to EFER generate the trap.
Then the "However" can be dropped from the start of the next sentence.
However, since the guest never explicitly sets the EFER_LMA bit, the
host never becomes aware that it has been set. This becomes problematic
when userspace tries to get/set the EFER values via
KVM_GET_SREGS/KVM_SET_SREGS, since the EFER contents tracked by the host
will be missing the EFER_LMA bit, and when userspace attempts to pass
the EFER value back via KVM_SET_SREGS it will fail a sanity check that
asserts that EFER_LMA should always be set when X86_CR0_PG and EFER_LME
are set.
Fix this by always inferring the value of EFER_LMA based on X86_CR0_PG
and EFER_LME, regardless of whether or not SEV-ES is enabled.
Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under SEV-ES")
Suggested-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
Acked-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
arch/x86/kvm/svm/svm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 5d75a1732da4..b31d4f2deb66 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1869,7 +1869,7 @@ void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
bool old_paging = is_paging(vcpu);
#ifdef CONFIG_X86_64
- if (vcpu->arch.efer & EFER_LME && !vcpu->arch.guest_state_protected) {
+ if (vcpu->arch.efer & EFER_LME) {
if (!is_paging(vcpu) && (cr0 & X86_CR0_PG)) {
vcpu->arch.efer |= EFER_LMA;
svm->vmcb->save.efer |= EFER_LMA | EFER_LME;
