From: Razvan Cojocaru <rcojocaru@bitdefender.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: andrew.cooper3@citrix.com, paul.durrant@citrix.com,
xen-devel@lists.xen.org
Subject: Re: [PATCH RFC] x86/emulate: implement hvmemul_cmpxchg() with an actual CMPXCHG
Date: Tue, 28 Mar 2017 13:50:02 +0300 [thread overview]
Message-ID: <f798ff03-9ca6-10e0-2a08-612de3d987c9@bitdefender.com> (raw)
In-Reply-To: <58DA5B7E020000780014900C@prv-mh.provo.novell.com>
On 03/28/2017 01:47 PM, Jan Beulich wrote:
>>>> On 28.03.17 at 12:27, <rcojocaru@bitdefender.com> wrote:
>> On 03/28/2017 01:03 PM, Jan Beulich wrote:
>>>>>> On 28.03.17 at 11:14, <rcojocaru@bitdefender.com> wrote:
>>>> I'm not sure that the RETRY model is what the guest OS expects. AFAIK, a
>>>> failed CMPXCHG should happen just once, with the proper registers and ZF
>>>> set. The guest surely expects neither that the instruction resume until
>>>> it succeeds, nor that some hidden loop goes on for an undeterminate
>>>> ammount of time until a CMPXCHG succeeds.
>>>
>>> The guest doesn't observe the CMPXCHG failing - RETRY leads to
>>> the instruction being restarted instead of completed.
>>
>> Indeed, but it works differently with hvm_emulate_one_vm_event() where
>> RETRY currently would have the instruction be re-executed (properly
>> re-executed, not just re-emulated) by the guest.
>
> Right - see my other reply to Andrew: The function likely would
> need to tell apart guest CMPXCHG uses from us using the insn to
> carry out the write by some other one. That may involve
> adjustments to the memory write logic in x86_emulate() itself, as
> the late failure of the comparison then would also need to be
> communicated back (via ZF clear) to the guest.
Exactly, it would require quite some reworking of x86_emulate().
Thanks,
Razvan
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next prev parent reply other threads:[~2017-03-28 10:50 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-24 13:24 [PATCH RFC] x86/emulate: implement hvmemul_cmpxchg() with an actual CMPXCHG Razvan Cojocaru
2017-03-28 9:14 ` Razvan Cojocaru
2017-03-28 10:03 ` Jan Beulich
2017-03-28 10:25 ` Andrew Cooper
2017-03-28 10:44 ` Jan Beulich
2017-03-29 5:59 ` Jan Beulich
2017-03-29 8:14 ` Razvan Cojocaru
2017-03-28 10:27 ` Razvan Cojocaru
2017-03-28 10:47 ` Jan Beulich
2017-03-28 10:50 ` Razvan Cojocaru [this message]
2017-03-28 11:32 ` Jan Beulich
2017-03-29 13:55 ` Jan Beulich
2017-03-29 14:00 ` Razvan Cojocaru
2017-03-29 15:04 ` Razvan Cojocaru
2017-03-29 15:49 ` Razvan Cojocaru
2017-03-30 12:05 ` Jan Beulich
2017-03-30 12:25 ` Razvan Cojocaru
2017-03-30 12:56 ` Razvan Cojocaru
2017-03-30 14:08 ` Razvan Cojocaru
2017-03-30 14:21 ` Jan Beulich
2017-03-30 15:05 ` Razvan Cojocaru
2017-03-30 15:47 ` Jan Beulich
2017-03-31 6:17 ` Razvan Cojocaru
2017-03-31 7:34 ` Jan Beulich
2017-03-31 9:56 ` Razvan Cojocaru
2017-03-31 14:46 ` Jan Beulich
2017-03-31 15:01 ` Razvan Cojocaru
2017-03-31 15:04 ` Jan Beulich
2017-04-01 16:56 ` Razvan Cojocaru
2017-04-03 10:23 ` Jan Beulich
2017-04-03 18:20 ` Razvan Cojocaru
2017-04-03 18:36 ` Razvan Cojocaru
2017-04-04 9:07 ` Jan Beulich
2017-04-04 12:01 ` Razvan Cojocaru
2017-04-08 22:15 ` Razvan Cojocaru
2017-04-09 11:03 ` Razvan Cojocaru
2017-04-10 10:18 ` Jan Beulich
2017-03-29 14:12 ` Razvan Cojocaru
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