Re: [Xen-devel] [PATCHv3 1/3] x86/fpu: improve check for XSAVE* not writing FIP/FDP fields

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/02/16 14:27, Jan Beulich wrote:
>>>> On 25.02.16 at 14:16, <andrew.cooper3@xxxxxxxxxx> 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.

~Andrew

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