Re: [PATCH 1/2][4.15?] x86/shadow: suppress "fast fault path" optimization when running virtualized

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.03.2021 16:47, Andrew Cooper wrote:
> On 05/03/2021 15:37, Jan Beulich wrote:
>> We can't make correctness of our own behavior dependent upon a
>> hypervisor underneath us correctly telling us the true physical address
>> with hardware uses. Without knowing this, we can't be certain reserved
>> bit faults can actually be observed. Therefore, besides evaluating the
>> number of address bits when deciding whether to use the optimization,
>> also check whether we're running virtualized ourselves.
> 
> I think it would be helpful to point out why we can't even probe at boot
> - the behaviour may genuinely change as we migrate, and if we ever end
> up on an IceLake system levelled down for compatibility with older CPUs,
> the "paddr_bits < PADDR_BITS" check will malfunction in an unsafe way.

I've added a sentence to this effect.

>> Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Thanks.

Jan