Re: [Xen-devel] [PATCH] x86: properly gate clearing of PKU feature

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.08.2019 15:21, Andrew Cooper wrote:
> On 29/08/2019 14:13, Jan Beulich wrote:
>> On 29.08.2019 12:46, Andrew Cooper wrote:
>>> On 29/08/2019 10:27, Jan Beulich wrote:
>>>> setup_clear_cpu_cap() is __init and hence may not be called post-boot.
>>>> Note that opt_pku nevertheless is not getting __initdata added - see
>>>> e.g. commit 43fa95ae6a ("mm: make opt_bootscrub non-init").
>>>>
>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>
>>> However, I'm tempted to suggest that this logic disappears entirely. 
>>> Given that we don't support it for PV guests, and can't without taking a
>>> CR4 write on toggle_kernel_mode(), all this actually controls is whether
>>> the bit finds its way into the HVM max policy.
>> Well, if you mean replacing opt_pku by an addition to
>> parse_xen_cpuid(), then I'll be happy to do that as a follow-on.
>> If there is another direction you've been considering, then
>> you'd have to at least outline it.
> 
> Well - I did say "disappear entirely".  I don't see it as having, or
> liable to gain, any useful purpose.
> 
> In reality, it was subsumed into cpuid= by my patch to allow all bits to
> be tweak-able.

Did you post this patch already (I don't seem to recall; I only recall
there being the plan to do this)?

Jan

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