From: David Vrabel <david.vrabel@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Jan Beulich <JBeulich@suse.com>
Cc: xen-devel@lists.xenproject.org
Subject: Re: [PATCHv3 1/3] x86/fpu: improve check for XSAVE* not writing FIP/FDP fields
Date: Thu, 25 Feb 2016 15:09:27 +0000 [thread overview]
Message-ID: <56CF1927.2030302@citrix.com> (raw)
In-Reply-To: <56CF18A3.4040004@citrix.com>
On 25/02/16 15:07, Andrew Cooper wrote:
> On 25/02/16 14:27, Jan Beulich wrote:
>>>>> On 25.02.16 at 14:16, <andrew.cooper3@citrix.com> wrote:
>>> No OS is plausibly going to hide non-IP information in FIP.
>>>
>>> If some theoretical OS does do something like that, there is always the
>>> override available.
>> But who says it needs to be an OS to do so? User mode code could
>> as much (and would imo even be more likely to do so, compared to
>> an OS).
>
> Why does this matter? We *cannot* make a perfect heuristic in this case.
>
> The new heuristic is wrong substantially less often than the old
> heuristic, so is an improvement.
Well, no. The current one is wrong 0.01% of the time[1], and is now
wrong 0.0100000000000000001% of the time. I would suggest that this
isn't a significant different.
Anyway, since it was trivial to reorder the series, I'm posting a v4
with this controversial patch at the end.
David
[1] Based on the number of XenServer test cases it breaks.
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next prev parent reply other threads:[~2016-02-25 15:09 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-25 10:58 [PATCHv3 0/3] x86: workaround inability to fully restore FPU state David Vrabel
2016-02-25 10:58 ` [PATCHv3 1/3] x86/fpu: improve check for XSAVE* not writing FIP/FDP fields David Vrabel
2016-02-25 11:32 ` Jan Beulich
2016-02-25 12:18 ` David Vrabel
2016-02-25 12:27 ` Jan Beulich
2016-02-25 12:49 ` David Vrabel
2016-02-25 13:16 ` Andrew Cooper
2016-02-25 14:27 ` Jan Beulich
2016-02-25 15:07 ` Andrew Cooper
2016-02-25 15:09 ` David Vrabel [this message]
2016-03-01 6:27 ` Tian, Kevin
2016-03-01 9:31 ` Jan Beulich
2016-02-25 10:58 ` [PATCHv3 2/3] x86/fpu: Add a per-domain field to set the width of FIP/FDP David Vrabel
2016-02-25 11:24 ` Jan Beulich
2016-02-25 11:38 ` David Vrabel
2016-02-25 11:55 ` Jan Beulich
2016-02-25 10:58 ` [PATCHv3 3/3] x86/hvm: add HVM_PARAM_X87_FIP_WIDTH David Vrabel
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