Re: [PATCH] x86: Drop opt_pku entirely

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.08.2023 15:21, Andrew Cooper wrote:
> On 21/06/2023 8:37 am, Jan Beulich wrote:
>> On 20.06.2023 19:47, Andrew Cooper wrote:
>>> --- a/CHANGELOG.md
>>> +++ b/CHANGELOG.md
>>> @@ -25,6 +25,9 @@ The format is based on [Keep a 
>>> Changelog](https://keepachangelog.com/en/1.0.0/)
>>>   - Add support for AVX512-FP16 on x86.
>>>   - On Arm, Xen supports guests running SVE/SVE2 instructions. (Tech 
>>> Preview)
>>>  
>>> +### Removed
>>> + - On x86, the "pku" command line option has been removed.  It has never
>>> +   behaved precisely as described, and redundant with "cpuid=no-pku".
>> Nit: Missing "was"?
> 
> Fixed
> 
>>
>>> --- a/docs/misc/xen-command-line.pandoc
>>> +++ b/docs/misc/xen-command-line.pandoc
>>> @@ -1950,16 +1950,6 @@ for all of them (`true`), only for those subject to 
>>> XPTI (`xpti`) or for
>>>  those not subject to XPTI (`no-xpti`). The feature is used only in case
>>>  INVPCID is supported and not disabled via `invpcid=false`.
>>>  
>>> -### pku (x86)
>>> -> `= <boolean>`
>>> -
>>> -> Default: `true`
>>> -
>>> -Flag to enable Memory Protection Keys.
>>> -
>>> -The protection-key feature provides an additional mechanism by which IA-32e
>>> -paging controls access to usermode addresses.
>>> -
>>>  ### ple_gap
>>>  > `= <integer>`
>> Elsewhere you said that we kind of imply that only the explicitly named
>> sub-options of cpuid= are supported. If that's the case (which could do
>> with saying more explicitly), you will want to add "pku" there in order
>> to not regress what is (deemed) supported.
> 
> I disagree.  I can say it was equivalent to X without X being an
> explicitly supported option.
> 
> PKU shouldn't be adjusted by either of these options; it should be
> controlled in the VM config file (if at all).  I'm unwilling to make any
> suggestion that this is supported.

Hmm, so you're suggesting "pku=" use was unsupported, too? If so, perhaps
worth adding the word "unsupported" to the CHANGELOG.md entry. At which
point I'm fine with no adjustment to cpuid= doc. And then also
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan