Re: [Xen-devel] [PATCH 7/8] xen/x86: Rework CR4 handling for PV guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.06.15 at 10:10, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 26/06/2015 07:22, Jan Beulich wrote:
>>>>> On 25.06.15 at 18:22, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> After recent consideration, I am still not sure if we want to support
>>> SMAP in 32bit PV guests or not.  The trapping of stac/clac would be a
>>> high overhead, although the guest could modify EFLAGS.AC itself using popf.
>> If it technically works (which it looks like it does) I see no reason
>> leaving the decision to guests.
> 
> True.  For now, I will leave SMAP/SMEP unexposed and leave the CPUID
> side of things to my levelling work.

In which case there's no point assuming an "aware" guest - with the
CPUID flag unexposed, writes to CR4.SMAP are simply invalid.

Jan


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