Re: [Xen-devel] [PATCH] VMX: don't crash processing 'd' debug key

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.11.13 at 20:08, Tim Deegan <tim@xxxxxxx> wrote:
> At 10:44 +0000 on 07 Nov (1383817496), Jan Beulich wrote:
>> @@ -675,7 +675,17 @@ void vmx_get_segment_register(struct vcp
>>  {
>>      unsigned long attr = 0, sel = 0, limit;
>>  
>> -    vmx_vmcs_enter(v);
>> +    /*
>> +     * We may get here in the context of dump_execstate(), which may have
>> +     * interrupted context switching between setting "current" and
>> +     * vmx_do_resume() reaching the end of vmx_load_vmcs(). That would make
>> +     * all the VMREADs below fail if we don't bail right away.
>> +     */
>> +    if ( unlikely(!vmx_vmcs_enter(v)) )
>> +    {
>> +        memset(reg, 0, sizeof(*reg));
>> +        return;
> 
> It would be nice to print something here, at least on the first
> instance.  Otherwise someone looking at bizarre debugkey output would
> have to know (and remember) about this path.

Did this.

> I'd also be inclined to ASSERT that, e.g. interrupts are disabled here
> -- if for any reason this function ever starts corrupting register
> state on other paths, we'll want to know about it quickly!

But I'm rather hesitant to do this. If anything, we'd need per-CPU
state tracking whether we're in do_invalid_op()'s main switch.

Jan


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