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Re: [Xen-devel] [PATCH] x86/MCE: bypass uninitialized vcpu in vMCE injection

On 05/08/2014 09:12 AM, Kai Huang wrote:

On 05/07/2014 09:25 PM, Egger, Christoph wrote:
On 07.05.14 09:29, Kai Huang wrote:
Dom0 may bring up less number of vCPUs than xen hypervisor actually created for it, and in this case, on Intel platform, vMCE injection to dom0 will fail due to
injecting vMCE to uninitialized vcpu, and cause dom0 crash.

Signed-off-by: Kai Huang <kai.huang@xxxxxxxxxxxxxxx>
  xen/arch/x86/cpu/mcheck/vmce.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/xen/arch/x86/cpu/mcheck/vmce.c b/xen/arch/x86/cpu/mcheck/vmce.c
index c83375e..72fe924 100644
--- a/xen/arch/x86/cpu/mcheck/vmce.c
+++ b/xen/arch/x86/cpu/mcheck/vmce.c
@@ -356,6 +356,10 @@ int inject_vmce(struct domain *d, int vcpu)
          if ( vcpu != VMCE_INJECT_BROADCAST && vcpu != v->vcpu_id )
+ /* In case of broadcasting, don't inject to uninitialized VCPU */
+        if ( vcpu == VMCE_INJECT_BROADCAST && !v->is_initialised )
+            continue;
What happens when you inject to exactly one uninitialized VCPU?
I think what you want is this:

            /* Don't inject to uninitialized VCPU */
            if ( !v->is_initialised )
Good suggestion indeed. In inject_vmce, the ret is initialized to -ESRCH at beginning. In case of injecting to one particular vcpu, we will simply bypass all loops of "for_each_vcpu" and don't do the injection at all, while the ret remains -ESRCH. Looks it's the right behaviour for AMD case.

Thanks Egger for comments (and sorry that I forgot to CC you at beginning:)). I'll follow your suggestion.
Hi Egger,

Forgot to say, the reason I didn't do this at beginning is this code will potentially impact vMCE injection behaviour on AMD platform. Considering I don't have AMD machine to test, so I can just do a theoretically analysis here. If you are OK with this, I'll follow your suggestion, Otherwise, I think Jan's suggestion is also good enough.


          if ( (has_hvm_container_domain(d) ||
guest_has_trap_callback(d, v->vcpu_id, TRAP_machine_check)) &&
               !test_and_set_bool(v->mce_pending) )

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