On 4/26/2023 4:26 PM, Anselm Busse wrote:
This patch adds a KVM vCPU stat that reflects the number of #AC
exceptions caused by a guest. This improves the identification and
debugging of issues that are possibly caused by guests triggering
split-locks and allows more insides compared to the current situation
of having only a warning printed when an #AC exception is raised.
Note, on Intel platform, #AC exception has three sources according to
the latest spec:
1. violation on alignment check when CPL = 3, while CR0.AM and EFLAG.AC
are set;
2. split lock, when MSR_MEMORY_CTRL.[29] is set;
3. UC lock, when CPUID.0x7_0x2:EDX[16] is 1 and
MSR_MEMORY_CTRL(0x33).[28] is 1. (see ISE version 048);
you cannot treat every #AC as split lock #AC.
Signed-off-by: Anselm Busse <abusse@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/vmx/vmx.c | 2 ++
arch/x86/kvm/x86.c | 1 +
3 files changed, 4 insertions(+)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 808c292ad3f4..b4ab719fbc69 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1523,6 +1523,7 @@ struct kvm_vcpu_stat {
u64 preemption_other;
u64 guest_mode;
u64 notify_window_exits;
+ u64 split_lock_exceptions;
};
struct x86_instruction_info;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d2d6e1b6c788..8f48fd8ddead 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5309,6 +5309,8 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
kvm_run->debug.arch.exception = ex_no;
break;
case AC_VECTOR:
+ vmx->vcpu.stat.split_lock_exceptions++;
+
if (vmx_guest_inject_ac(vcpu)) {
kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
return 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3d852ce84920..416a1ed6c423 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -297,6 +297,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
STATS_DESC_COUNTER(VCPU, preemption_other),
STATS_DESC_IBOOLEAN(VCPU, guest_mode),
STATS_DESC_COUNTER(VCPU, notify_window_exits),
+ STATS_DESC_COUNTER(VCPU, split_lock_exceptions),
};
const struct kvm_stats_header kvm_vcpu_stats_header = {
