Re: [Xen-devel] vmx_update_guest_cr() losing EXCEPTION_BITMAP setting

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

Ah, I see. Well I can do a cleaner patch than that I think, so I'll sort
that out and check it in.

 -- Keir

On 11/05/2009 18:21, "Byrne, John (HP Labs)" <john.l.byrne@xxxxxx> wrote:

> 
> I had hit upon the fix of clearing v->arch.hvm_vcpu.debug_state_latch=0 and
> this had apparently fixed the problem I was seeing. However, reviewing the
> code, the schedule_softirq(SECHDULE_SOFTIRQ) you added looks necessary for a
> complete fix. A caveat: I am not running a domain-debugger, I am just
> borrowing the code for my lockstep work. I don't see why the fix wouldn't work
> in that case, but I'm not testing it.
> 
> John
> 
> 
>> -----Original Message-----
>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>> Sent: Monday, May 11, 2009 10:15 AM
>> To: Byrne, John (HP Labs)
>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>> Subject: Re: [Xen-devel] vmx_update_guest_cr() losing EXCEPTION_BITMAP
>> setting
>> 
>> Very cryptic. Did it fix the bug you originally posted about?
>> 
>>  -- Keir
>> 
>> On 11/05/2009 17:05, "Byrne, John (HP Labs)" <john.l.byrne@xxxxxx>
>> wrote:
>> 
>>> The schedule_softirq() does close a hole I wasn't noticing.
>>> 
>>> Thanks.
>>> 
>>>> -----Original Message-----
>>>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>>>> Sent: Sunday, May 10, 2009 11:52 PM
>>>> To: Byrne, John (HP Labs); xen-devel@xxxxxxxxxxxxxxxxxxx
>>>> Subject: Re: [Xen-devel] vmx_update_guest_cr() losing
>> EXCEPTION_BITMAP
>>>> setting
>>>> 
>>>> On 11/05/2009 05:32, "Byrne, John (HP Labs)" <john.l.byrne@xxxxxx>
>>>> wrote:
>>>> 
>>>>> Running a heavily modified xen-unstable changset 19590:f80cf52a4fb6
>>>> with
>>>>> debugger_attached set, I was seeing the debug traps getting lost
>> from
>>>> the
>>>>> EXCEPTION_BITMAP in vmx_update_guest_cr() when transitioning from
>>>> real to
>>>>> protected mode.  In my codebase, I could fix this trivially by
>>>> clearing the
>>>>> debug_state_latch and letting vmx_do_resume() reapply the setting.
>>>> However,
>>>>> while it looks like a valid issue in the unmodified codebase, I'm
>> not
>>>> sure. So
>>>>> maybe someone might test/examine it and decide if it is real and
>>>> whether some
>>>>> more complex fix is required?
>>>> 
>>>> In vmx_update_guest_cr(), where EXCEPTION_BITMAP gets reset after
>> exit
>>>> from
>>>> real mode, try setting v->arch.hvm_vcpu.debug_state_latch=0 and
>>>> raise_softirq(SCHEDULE_SOFTIRQ).
>>>> 
>>>>  -- Keir
>>>> 
>>> 
>> 
> 



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