From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Two types #AC can be generated in Intel CPUs:
1. legacy alignment check #AC
2. split lock #AC
Reflect #AC back into the guest if the guest has legacy alignment checks
enabled or if SLD is disabled. If SLD is enabled, treat the guest like
a host userspace application by calling handle_user_split_lock(). If
the #AC is handled (SLD disabled and TIF_SLD set), then simply resume
the guest. If the #AC isn't handled, i.e. host is sld_fatal, then
forward the #AC to the userspace VMM, similar to sending SIGBUS.
Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 30 +++++++++++++++++++++++++++---
1 file changed, 27 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 458e684dfbdc..a96cfda0a5b9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4623,6 +4623,12 @@ static int handle_machine_check(struct kvm_vcpu *vcpu)
return 1;
}
+static inline bool guest_cpu_alignment_check_enabled(struct kvm_vcpu *vcpu)
+{
+ return vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) &&
+ (kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
+}
+
static int handle_exception_nmi(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -4688,9 +4694,6 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
return handle_rmode_exception(vcpu, ex_no, error_code);
switch (ex_no) {
- case AC_VECTOR:
- kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
- return 1;
case DB_VECTOR:
dr6 = vmcs_readl(EXIT_QUALIFICATION);
if (!(vcpu->guest_debug &
@@ -4719,6 +4722,27 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
kvm_run->debug.arch.exception = ex_no;
break;
+ case AC_VECTOR:
+ /*
+ * Reflect #AC to the guest if it's expecting the #AC, i.e. has
+ * legacy alignment check enabled. Pre-check host split lock
+ * turned on to avoid the VMREADs needed to check legacy #AC,
+ * i.e. reflect the #AC if the only possible source is legacy
+ * alignment checks.
+ */
+ if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) ||
+ guest_cpu_alignment_check_enabled(vcpu)) {
+ kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
+ return 1;
+ }
+
+ /*
+ * Forward the #AC to userspace if kernel policy does not allow
+ * temporarily disabling split lock detection.
+ */
+ if (handle_user_split_lock(kvm_rip_read(vcpu)))
+ return 1;
+ fallthrough;
default:
kvm_run->exit_reason = KVM_EXIT_EXCEPTION;
kvm_run->ex.exception = ex_no;
--
2.24.1
