[PATCH] Ignore SRAO MCE if another MCE is being processed

[Huang Ying <ying.huang@xxxxxxxxx>]

In common cases, guest SRAO MCE will cause corresponding poisoned page
be un-mapped in host and SIGBUS be sent to QEMU-KVM, then QEMU-KVM
will relay the MCE to guest OS.

But it is possible that the poisoned page is accessed in guest after
un-mapped in host and before MCE is relayed to guest OS. So that, the
SRAR SIGBUS is sent to QEMU-KVM before the SRAO SIGBUS, and if
QEMU-KVM relays them to guest OS one by one, guest system may reset,
because the SRAO MCE may be triggered while the SRAR MCE is being
processed. In fact, the SRAO MCE can be ignored in this situation, so
that the guest system is given opportunity to survive.

Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx>
---
 qemu-kvm.c |   28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -1610,6 +1610,19 @@ static void flush_queued_work(CPUState *
     pthread_cond_broadcast(&qemu_work_cond);
 }
 
+static int kvm_mce_in_exception(CPUState *env)
+{
+    struct kvm_msr_entry msr_mcg_status = {
+        .index = MSR_MCG_STATUS,
+    };
+    int r;
+
+    r = kvm_get_msrs(env, &msr_mcg_status, 1);
+    if (r == -1 || r == 0)
+        return -1;
+    return !!(msr_mcg_status.data & MCG_STATUS_MCIP);
+}
+
 static void kvm_on_sigbus(CPUState *env, siginfo_t *siginfo)
 {
 #if defined(KVM_CAP_MCE) && defined(TARGET_I386)
@@ -1630,6 +1643,15 @@ static void kvm_on_sigbus(CPUState *env,
             mce.misc = (MCM_ADDR_PHYS << 6) | 0xc;
             mce.mcg_status = MCG_STATUS_MCIP | MCG_STATUS_EIPV;
         } else {
+            /*
+             * If there is an MCE excpetion being processed, ignore
+             * this SRAO MCE
+             */
+            r = kvm_mce_in_exception(env);
+            if (r == -1)
+                fprintf(stderr, "Failed to get MCE status\n");
+            else if (r)
+                return;
             /* Fake an Intel architectural Memory scrubbing UCR */
             mce.status = MCI_STATUS_VAL | MCI_STATUS_UC | MCI_STATUS_EN
                 | MCI_STATUS_MISCV | MCI_STATUS_ADDRV | MCI_STATUS_S
@@ -2475,6 +2497,12 @@ static void kvm_do_inject_x86_mce(void *
     struct kvm_x86_mce_data *data = _data;
     int r;
 
+    /* If there is an MCE excpetion being processed, ignore this SRAO MCE */
+    r = kvm_mce_in_exception(data->env);
+    if (r == -1)
+        fprintf(stderr, "Failed to get MCE status\n");
+    else if (r && !(data->mce->status & MCI_STATUS_AR))
+        return;
     r = kvm_set_mce(data->env, data->mce);
     if (r < 0) {
         perror("kvm_set_mce FAILED");


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