[Xen-devel] RE: [PATCH] Don't enable irq for machine check vmexit

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Keir, any comments to this patch?

Thanks
Yunhong Jiang

>-----Original Message-----
>From: Jiang, Yunhong
>Sent: Monday, February 01, 2010 5:18 PM
>To: Jiang, Yunhong; Keir Fraser; Tim.Deegan@xxxxxxxxxx
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: RE: [PATCH] Don't enable irq for machine check vmexit
>
>Sorry forgot the patch.
>
>--jyh
>
>diff -r 857d7b2dd8c7 xen/arch/x86/hvm/vmx/vmx.c
>--- a/xen/arch/x86/hvm/vmx/vmx.c       Fri Jan 29 08:59:46 2010 +0000
>+++ b/xen/arch/x86/hvm/vmx/vmx.c       Sun Jan 31 18:40:34 2010 +0800
>@@ -2153,6 +2153,7 @@ static void vmx_failed_vmentry(unsigned
>         printk("caused by machine check.\n");
>         HVMTRACE_0D(MCE);
>         do_machine_check(regs);
>+        local_irq_enable();
>         break;
>     default:
>         printk("reason not known yet!");
>@@ -2243,6 +2244,23 @@ err:
> err:
>     vmx_inject_hw_exception(TRAP_gp_fault, 0);
>     return -1;
>+}
>+
>+int vmx_mce_exit(int exit_reason)
>+{
>+    if ( unlikely(exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY &&
>+        (uint16_t)exit_reason == EXIT_REASON_MCE_DURING_VMENTRY) )
>+            return 1;
>+    else if (unlikely(exit_reason == EXIT_REASON_EXCEPTION_NMI))
>+    {
>+        uint32_t vector;
>+
>+        vector = __vmread(VM_EXIT_INTR_INFO) & INTR_INFO_VECTOR_MASK;
>+        if (vector == TRAP_machine_check)
>+            return 1;
>+    }
>+
>+    return 0;
> }
>
> asmlinkage void vmx_vmexit_handler(struct cpu_user_regs *regs)
>@@ -2273,7 +2291,8 @@ asmlinkage void vmx_vmexit_handler(struc
>         vmx_do_extint(regs);
>
>     /* Now enable interrupts so it's safe to take locks. */
>-    local_irq_enable();
>+    if ( !(vmx_mce_exit(exit_reason)) )
>+        local_irq_enable();
>
>     if ( unlikely(exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) )
>         return vmx_failed_vmentry(exit_reason, regs);
>@@ -2433,6 +2452,7 @@ asmlinkage void vmx_vmexit_handler(struc
>         case TRAP_machine_check:
>             HVMTRACE_0D(MCE);
>             do_machine_check(regs);
>+            local_irq_enable();
>             break;
>         case TRAP_invalid_op:
>             vmx_vmexit_ud_intercept(regs);
>
>
>
>>-----Original Message-----
>>From: Jiang, Yunhong
>>Sent: Monday, February 01, 2010 4:48 PM
>>To: Keir Fraser; Tim.Deegan@xxxxxxxxxx
>>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>>Subject: [PATCH] Don't enable irq for machine check vmexit
>>
>>We should not enable irq for machine check VMExit
>>
>>In changeset 18658:824892134573, IRQ is enabled during VMExit except external
>>interrupt. The exception should apply for machine check also, because :
>>a) The mce_logout_lock should be held in irq_disabled context.
>>b) The machine check event should be handled as quickly as possible, enable 
>>irq will
>>increase the period greatly.
>>
>>Signed-off-by: Jiang, Yunhong <yunhong.jiang@xxxxxxxxx>
>>
>>This is in hotspot code path, I try to use unlikely, hope to reduce the 
>>performance
>>impact
>>
>>Thanks
>>Yunhong Jiang


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