Re: [Xen-devel] [PATCH v2 1/2] x86: Meltdown band-aid against malicious 64-bit PV guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.01.18 at 12:56, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/01/18 09:33, Jan Beulich wrote:
>>>>> On 15.01.18 at 19:23, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 15/01/18 11:06, Jan Beulich wrote:
>>>> This also wants Andrew's "[PATCH RFC 11/44] x86/pt-shadow: Always set
>>>> _PAGE_ACCESSED on L4e updates".
>>> I've cleaned this patch up and committed it in preparation.
>>>
>>> http://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=bd61fe94bee0556bc2f6
>>>  
> 
>>> 4999a4a8315b93f90f21
>> Only now that I'm doing backports thereof I notice an oddity with
>> 32-bit guest handling: Why would you set the accessed bit in that
>> case? The L4 is an internal thing there, and hence by us knowing
>> that we don't care, this is unnecessary (but of course also not
>> wrong). I'll do the 4.9 and older backports according to that
>> observation (making for slightly less of a code change).
> 
> There are no paths leading to adjust_guest_l4e() for 32bit PV guests. 
> The only L4 handling which exists is constructing the monitor table,
> which writes the PTEs directly.

Yeah, I did realize this after writing. The check could probably
go away altogether.

Jan


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