On 10/08/21 23:21, Maxim Levitsky wrote:
On Tue, 2021-08-10 at 23:52 +0300, Maxim Levitsky wrote:
Hi!
This is a series of bugfixes to the AVIC dynamic inhibition, which was
made while trying to fix bugs as much as possible in this area and trying
to make the AVIC+SYNIC conditional enablement work.
* Patches 1,3-8 are code from Sean Christopherson which
I mean patches 1,4-8. I forgot about patch 3 which I also added,
which just added a comment about parameters of the kvm_flush_remote_tlbs_with_address.
Best regards,
Maxim Levitsky
implement an alternative approach of inhibiting AVIC without
disabling its memslot.
V4: addressed review feedback.
* Patch 2 is new and it fixes a bug in kvm_flush_remote_tlbs_with_address
* Patches 9-10 in this series fix a race condition which can cause
a lost write from a guest to APIC when the APIC write races
the AVIC un-inhibition, and add a warning to catch this problem
if it re-emerges again.
V4: applied review feedback from Paolo
* Patch 11 is the patch from Vitaly about allowing AVIC with SYNC
as long as the guest doesn’t use the AutoEOI feature. I only slightly
changed it to expose the AutoEOI cpuid bit regardless of AVIC enablement.
V4: fixed a race that Paolo pointed out.
* Patch 12 is a refactoring that is now possible in SVM AVIC inhibition code,
because the RCU lock is not dropped anymore.
* Patch 13-15 fixes another issue I found in AVIC inhibit code:
Currently avic_vcpu_load/avic_vcpu_put are called on userspace entry/exit
from KVM (aka kvm_vcpu_get/kvm_vcpu_put), and these functions update the
"is running" bit in the AVIC physical ID remap table and update the
target vCPU in iommu code.
However both of these functions don't do anything when AVIC is inhibited
thus the "is running" bit will be kept enabled during the exit to userspace.
This shouldn't be a big issue as the caller
doesn't use the AVIC when inhibited but still inconsistent and can trigger
a warning about this in avic_vcpu_load.
To be on the safe side I think it makes sense to call
avic_vcpu_put/avic_vcpu_load when inhibiting/uninhibiting the AVIC.
This will ensure that the work these functions do is matched.
V4: I splitted a single patch to 3 patches to make it easier
to review, and applied Paolo's review feedback.
* Patch 16 removes the pointless APIC base
relocation from AVIC to make it consistent with the rest of KVM.
(both AVIC and APICv only support default base, while regular KVM,
sort of support any APIC base as long as it is not RAM.
If guest attempts to relocate APIC base to non RAM area,
while APICv/AVIC are active, the new base will be non accelerated,
while the default base will continue to be AVIC/APICv backed).
On top of that if guest uses different APIC bases on different vCPUs,
KVM doesn't honour the fact that the MMIO range should only be active
on that vCPU.
No problem, b4 diff is my friend. :) Queued, thanks.
Paolo
