Re: [Xen-devel] [PATCH 1/2] x86/mm: Change default value for suppress #VE in set_mem_access()

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Thu, Jun 15, 2017 at 7:49 PM, Tamas K Lengyel <tamas@xxxxxxxxxxxxx> wrote:
> On Fri, Jun 9, 2017 at 10:51 AM, Adrian Pop <apop@xxxxxxxxxxxxxxx> wrote:
>> From: Vlad Ioan Topan <itopan@xxxxxxxxxxxxxxx>
>>
>> The default value for the "suppress #VE" bit set by set_mem_access()
>> currently depends on whether the call is made from the same domain (the
>> bit is set when called from another domain and cleared if called from
>> the same domain). This patch changes that behavior to inherit the old
>> suppress #VE bit value if it is already set and to set it to 1
>> otherwise, which is safer and more reliable.
>
> Could you elaborate on why do you think it is safer and more reliable
> to switch the behavior? I believe the original idea was that the
> domain should only be allowed to clear an SVE bit set by an external
> tool. With this change it will allow the guest to request VE for any
> page the external tool hasn't itself reserved specifically.

Hmm?  This patch by itself simply prevents the guest from changing the
VE bit at all (either setting or clearing it).

Or did you mean, "This patch series"?

 -George

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