Messages in this thread | | | Date | Mon, 18 Oct 2021 21:31:19 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL |
| |
On Mon, Oct 18, 2021 at 12:10:20PM -0700, H. Peter Anvin wrote: > AFAIK no Intel CPU has ever had that behavior, and always cleared the > segments; I don't Intel has any plans of supporting such a CPUID bit > (although I'd certainly be willing to take such a request back to the > CPU teams on request.)
No need - we can always set or clear a flag on Intel, depending on what we do.
> That being said, this sounds like an ideal use for the hypervisor CPU > feature flag.
Yap, it uses it.
> Maybe we should consider a migration hypervisor flag too to explicitly > tell the kernel not to rely on hardware probing that breaks migration > in general.
Meh, migration-specific flag calls for all kinds of nasty when each HV would want different things to happen in the guest, for migration. And then the patch flood will come. I mean, we already do a bunch of X86_FEATURE_HYPERVISOR all over the place and apparently it is enough here too...
> Now, with a CPUID but being introduced, the right thing would be to > use the CPUID bit as a feature instead of using a bug flag, and add > whitelisting in the vendor-specific code as applicable.
I guess we can flip all that logic checking X86_BUG_NULL_SEG... it sounds like a lot of churn to me, though and I don't see a pressing need for it unless someone is bored and wants to do some kernel patching exercises but whatever...
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
| |