Re: [PATCH v3 08/12] KVM: Propagate vcpu explicitly to mark_page_dirty_in_slot()
From: "David Woodhouse" <dwmw2@infradead.org>
Date: 2021-11-17 21:12:23
Also in:
kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-mips, linux-s390
From: David Woodhouse <redacted>
The kvm_dirty_ring_get() function uses kvm_get_running_vcpu() to work out
which dirty ring to use, but there are some use cases where that doesn't
work.
There's one in setting the Xen shared info page, introduced in commit
629b5348841a ("KVM: x86/xen: update wallclock region") and reported by
"butt3rflyh4ck" [off-list ref] in
https://lore.kernel.org/kvm/CAFcO6XOmoS7EacN_n6v4Txk7xL7iqRa2gABg3F7E3Naf5uG94g@mail.gmail.com/ (local)
There's also about to be another one when the newly-reintroduced
gfn_to_pfn_cache needs to mark a page as dirty from the MMU notifier
which invalidates the mapping. In that case, we will *know* the vcpu
that can be 'blamed' for dirtying the page, and we just need to be
able to pass it in as an explicit argument when doing so.
This patch preemptively resolves the second issue, and paves the way
for resolving the first. A complete fix for the first issue will need
us to switch the Xen shinfo to be owned by a particular vCPU, which
will happen in a separate patch.
Signed-off-by: David Woodhouse <redacted>quoted hunk ↗ jump to hunk
--- a/virt/kvm/dirty_ring.c +++ b/virt/kvm/dirty_ring.c@@ -36,12 +36,16 @@ static bool kvm_dirty_ring_full(struct kvm_dirty_ring*ring) return kvm_dirty_ring_used(ring) >= ring->size; } -struct kvm_dirty_ring *kvm_dirty_ring_get(struct kvm *kvm) +struct kvm_dirty_ring *kvm_dirty_ring_get(struct kvm *kvm, struct kvm_vcpu *vcpu) { - struct kvm_vcpu *vcpu = kvm_get_running_vcpu(); + struct kvm_vcpu *running_vcpu = kvm_get_running_vcpu(); + WARN_ON_ONCE(vcpu && vcpu != running_vcpu); WARN_ON_ONCE(vcpu->kvm != kvm);
Ah, that one needs to be changed to check running_vcpu instead. Or this needs to go first: I think I prefer making the vCPU a required argument. If anyone's going to pull a vCPU pointer out of their posterior, let the caller do it.
+ if (!vcpu) + vcpu = running_vcpu; + return &vcpu->dirty_ring; }
-- dwmw2