From: David Vrabel <david.vrabel@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
David Vrabel <david.vrabel@citrix.com>,
xen-devel@lists.xenproject.org
Cc: Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCHv2 1/3] x86/fpu: improve check for XSAVE* not writing FIP/FDP fields
Date: Tue, 23 Feb 2016 11:54:16 +0000 [thread overview]
Message-ID: <56CC4868.8040504@citrix.com> (raw)
In-Reply-To: <56CC3FE8.4000805@citrix.com>
On 23/02/16 11:18, Andrew Cooper wrote:
> On 23/02/16 11:05, David Vrabel wrote:
>> The hardware may not write the FIP/FDP fields with a XSAVE*
>> instruction. e.g., with XSAVEOPT/XSAVES if the state hasn't changed
>> or on AMD CPUs when a floating point exception is not pending. We
>> need to identify this case so we can correctly apply the check for
>> whether to save/restore FCS/FDS.
>>
>> By toggling FIP[63] we can turn the field into a non-canonical address
>> and check for this value after the XSAVE instruction.
>>
>> This results in smaller code with fewer branches and is more
>> understandable.
>>
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>
> For consistently, the same change in detection logic should be applied
> to fpu_fxsave()
I don't think it is necessary. fpu_fxsave() only needs to check for the
AMD case, and the logic is already simple.
David
next prev parent reply other threads:[~2016-02-23 11:54 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 11:05 [PATCHv2 0/3] x86: workaround inability to fully restore FPU state David Vrabel
2016-02-23 11:05 ` [PATCHv2 1/3] x86/fpu: improve check for XSAVE* not writing FIP/FDP fields David Vrabel
2016-02-23 11:18 ` Andrew Cooper
2016-02-23 11:54 ` David Vrabel [this message]
2016-02-23 14:07 ` Jan Beulich
2016-02-23 14:59 ` Jan Beulich
2016-02-23 17:42 ` David Vrabel
2016-02-24 7:51 ` Jan Beulich
2016-02-24 10:37 ` Tian, Kevin
2016-02-24 10:49 ` Jan Beulich
2016-03-18 18:23 ` Lai, Paul C
2016-02-23 11:05 ` [PATCHv2 2/3] x86/fpu: Add a per-domain field to set the width of FIP/FDP David Vrabel
2016-02-23 11:10 ` Andrew Cooper
2016-02-23 11:53 ` David Vrabel
2016-02-23 15:24 ` Jan Beulich
2016-02-23 16:27 ` David Vrabel
2016-02-23 16:39 ` Jan Beulich
2016-02-23 11:05 ` [PATCHv2 3/3] x86/hvm: add HVM_PARAM_X87_FIP_WIDTH David Vrabel
2016-02-23 11:20 ` Andrew Cooper
2016-02-24 11:51 ` Wei Liu
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