Hi Igor, On Wed, Jul 24, 2024 at 02:54:32PM +0200, Igor Mammedov wrote: > Date: Wed, 24 Jul 2024 14:54:32 +0200 > From: Igor Mammedov <imamm...@redhat.com> > Subject: Re: [PATCH v1] target/i386: Always set leaf 0x1f > X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-redhat-linux-gnu) > > 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 > > > > - 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.
So that in the future every new Intel CPU model will need to always enable 0x1f. Sounds like an endless game. So my question is: at what point is it ok to consider defaulting to always enable 0x1f and just disable it for the old CPU model? Thanks, Zhao
