On 8/24/23 20:36, Sean Christopherson wrote:
Treat EMULTYPE_SKIP failures on SEV guests as unhandleable emulation
instead of simply resuming the guest, and drop the hack-a-fix which
effects that behavior for the INT3/INTO injection path. If KVM can't
skip an instruction for which KVM has already done partial emulation,
resuming the guest is undesirable as doing so may corrupt guest state.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/svm/svm.c | 12 +-----------
arch/x86/kvm/x86.c | 9 +++++++--
2 files changed, 8 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 39ce680013c4..fc2cd5585349 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -364,8 +364,6 @@ static void svm_set_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
svm->vmcb->control.int_state |= SVM_INTERRUPT_SHADOW_MASK;
}
-static int svm_check_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
- void *insn, int insn_len);
static int __svm_skip_emulated_instruction(struct kvm_vcpu *vcpu,
bool commit_side_effects)
@@ -386,14 +384,6 @@ static int __svm_skip_emulated_instruction(struct kvm_vcpu *vcpu,
}
if (!svm->next_rip) {
- /*
- * FIXME: Drop this when kvm_emulate_instruction() does the
- * right thing and treats "can't emulate" as outright failure
- * for EMULTYPE_SKIP.
- */
- if (svm_check_emulate_instruction(vcpu, EMULTYPE_SKIP, NULL, 0) != X86EMUL_CONTINUE)
- return 0;
-
if (unlikely(!commit_side_effects))
old_rflags = svm->vmcb->save.rflags;
@@ -4752,7 +4742,7 @@ static int svm_check_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
*/
if (unlikely(!insn)) {
if (emul_type & EMULTYPE_SKIP)
- return X86EMUL_RETRY_INSTR;
+ return X86EMUL_UNHANDLEABLE;
Trying to follow this, bear with me...
This results in an "emulation failure" which fills out all the KVM
userspace exit information in prepare_emulation_failure_exit(). But
because of the return 0 in handle_emulation_failure(), in the end this
ends up just acting like the first patch because we exit out
svm_update_soft_interrupt_rip() early and the instruction just gets retried?
Thanks,
Tom
kvm_queue_exception(vcpu, UD_VECTOR);
return X86EMUL_PROPAGATE_FAULT;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f897d582d560..1f4a8fbc5390 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8858,8 +8858,13 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
bool writeback = true;
r = kvm_check_emulate_insn(vcpu, emulation_type, insn, insn_len);
- if (r != X86EMUL_CONTINUE)
- return 1;
+ if (r != X86EMUL_CONTINUE) {
+ if (r == X86EMUL_RETRY_INSTR || r == X86EMUL_PROPAGATE_FAULT)
+ return 1;
+
+ WARN_ON_ONCE(r != X86EMUL_UNHANDLEABLE);
+ return handle_emulation_failure(vcpu, emulation_type);
+ }
vcpu->arch.l1tf_flush_l1d = true;
