Re: [Xen-devel] [PATCH 00/10] x86/hvm: pkeys, add memory protection-key support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.11.15 at 17:24, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 17/11/15 10:26, Jan Beulich wrote:
>>>>> On 16.11.15 at 18:45, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> Furthermore, it is unclear (given the unwritten ABI) whether it is even
>>> safe to move _PAGE_GNTTAB out of the way, as this is visible to a PV guest.
>> It seems pretty clear to me that this would be unsafe: It being
>> part of L1_DISALLOW_MASK, if it moved and a guest used the
>> bit for its own purposes, the guest would break. I guess we'll
>> need an ELF note by which the guest can advertise which of the
>> available bits it doesn't care about itself.
> 
> Well - it depends whether any of these bits actually get used.
> 
> If none actually do get used, we would be better to retro-fit a real ABI
> in place, without requiring all new guests to opt-in to get new features.

And how exactly do you propose we check _all_ existing kernels?

Jan


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