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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew

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