On 24/07/24 6:24 pm, Igor Mammedov wrote:
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On Wed, 24 Jul 2024 12:13:28 +0100
John Levon <john.le...@nutanix.com> wrote:
On Wed, Jul 24, 2024 at 03:59:29PM +0530, Manish wrote:
Leaf 0x1f is superset of 0xb, so it makes sense to set 0x1f equivalent
to 0xb by default and workaround windows issue.>
This change adds a
new property 'cpuid-0x1f-enforce' to set leaf 0x1f equivalent to 0xb in
case extended CPU topology is not configured and behave as before otherwise.
repeating question
why we need to use extra property instead of just adding 0x1f leaf for CPU
models
that supposed to have it?
As i mentioned in earlier response. "Windows expects it only when we have
set max cpuid level greater than or equal to 0x1f. I mean if it is exposed
it should not be all zeros. SapphireRapids CPU definition raised cpuid level
to 0x20, so we starting seeing it with SapphireRapids."
Windows does not expect 0x1f to be present for any CPU model. But if it is
exposed to the guest, it expects non-zero values.
I think Igor is suggesting:
- leave x86_cpu_expand_features() alone completely
yep, drop that if possible
This was suggested by Zhao, probably could related to TDX work
mentioned? As i did not see any harm, i did not mind changing it.
- change the 0x1f handling to always report topology i.e. never report all
zeroes
Do this but only for CPU models that have this leaf per spec,
to avoid live migration issues create a new version of CPU model,
so it would apply only for new version. This way older versions
and migration won't be affected.
Yes, I can do that too. But i beleive it may not be a CPU model related
property or bug. What if someone uses older CPU model but explicitily
passes some extra flags to include 0x1f?
Yes, that would mean that if something requests 0x1f leaf even though the max
leaf is lower, they'd get data back, but it's not clear why that'd be an issue?
regards
john
Thanks
Manish Mishra
