Messages in this thread | | | Date | Tue, 9 Apr 2024 08:56:28 +0100 | Subject | Re: [PATCH v2] x86/mm: Don't disable INVLPG if "incomplete Global INVLPG flushes" is fixed by microcode | From | Andrew Cooper <> |
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On 09/04/2024 2:43 am, Sean Christopherson wrote: > On Mon, Apr 08, 2024, Michael Kelley wrote: >> From: Dave Hansen <dave.hansen@intel.com> Sent: Thursday, April 4, 2024 11:09 AM >>> On 4/4/24 10:48, Michael Kelley wrote: >>>> I agree one could argue that it is a hypervisor bug to present PCID to the guest >>>> in this situation. It's a lot cleaner to not have a guest be checking FMS and >>>> microcode versions. But whether that's practical in the real world, at least >>>> for Hyper-V, I don't know. What's the real impact of running with PCID while >>>> the flaw is still present? I don’t know the history here ... >>> There's a chance that INVLPG will appear ineffective. >>> >>> The bad sequence would go something like this: The kernel does the >>> INVLPG on a global mapping. Later, when switching PCIDs, the TLB entry >>> mysteriously reappears. No PCIDs switching means no mysterious >>> reappearance. >> Xi Ruoyao's patch identifies these errata: RPL042 and ADL063. In the links >> to the documents Xi provided, both of these errata have the following >> statement in the Errata Details section: >> >> This erratum does not apply in VMX non-root operation. It applies only >> when PCIDs are enabled and either in VMX root operation or outside >> VMX operation. >> >> I don't have deep expertise on the terminology here, but this sounds >> like it is saying the erratum doesn’t apply in a guest VM. Or am I >> misunderstanding? > Huh. My read of that is the same as yours. If that's the case, then it probably > makes sense to have KVM advertise support if PCID is available in hardware, even > if PCID is disabled by the host kernel.
My reading is the same also. Seems like VMs are fine.
~Andrew
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