Re: [PATCH] tools/guest: Fix comment regarding CPUID compatibility

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.02.2022 13:12, Andrew Cooper wrote:
> On 04/02/2022 08:31, Jan Beulich wrote:
>> On 03.02.2022 19:10, Andrew Cooper wrote:
>>> It was Xen 4.14 where CPUID data was added to the migration stream, and 4.13
>>> that we need to worry about with regards to compatibility.  Xen 4.12 isn't
>>> relevant.
>>>
>>> Expand and correct the commentary.
>>>
>>> Fixes: 111c8c33a8a1 ("x86/cpuid: do not expand max leaves on restore")
>> But doesn't this commit amend 685e922d6f30 ("tools/libxc: Rework
>> xc_cpuid_apply_policy() to use {get,set}_cpu_policy()"), which is
>> where DEF_MAX_* disappeared?
> 
> No. All that happened in that change was that we switched to using
> 
> cpuid.h:89:#define CPUID_GUEST_NR_EXTD_AMD
> 
> instead, which remained the same size until Xen 4.15 when e9b4fe26364
> bumped it.

Oh, right. I did try to look for a replacement, but managed to miss
this. But then, as much as 4.12 isn't relevant, isn't it the case
that the fact that CPUID data was added to the stream in 4.14 isn't
relevant here either, and it's instead the bumping in 4.15 which is?
IOW while I've been fine with the comment adjustment anyway, there
would still want to be an adjustment to the description.

>> While looking at this, wasn't Roger's change incomplete, in that
>> for Intel the extended leaf upper bound was 0x80000008 in 4.12?
> 
> CPUID_GUEST_NR_EXTD_INTEL is still 8, so this is all fine.

Again, somehow I did manage to miss the replacement defines.

Jan