Messages in this thread |  | | Date | Tue, 26 Oct 2021 16:41:05 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH v2 10/43] KVM: arm64: Move vGIC v4 handling for WFI out arch callback hook |
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On Mon, 25 Oct 2021 14:31:48 +0100, Paolo Bonzini <pbonzini@redhat.com> wrote: > > On 09/10/21 04:12, Sean Christopherson wrote: > > Move the put and reload of the vGIC out of the block/unblock callbacks > > and into a dedicated WFI helper. Functionally, this is nearly a nop as > > the block hook is called at the very beginning of kvm_vcpu_block(), and > > the only code in kvm_vcpu_block() after the unblock hook is to update the > > halt-polling controls, i.e. can only affect the next WFI. > > > > Back when the arch (un)blocking hooks were added by commits 3217f7c25bca > > ("KVM: Add kvm_arch_vcpu_{un}blocking callbacks) and d35268da6687 > > ("arm/arm64: KVM: arch_timer: Only schedule soft timer on vcpu_block"), > > the hooks were invoked only when KVM was about to "block", i.e. schedule > > out the vCPU. The use case at the time was to schedule a timer in the > > host based on the earliest timer in the guest in order to wake the > > blocking vCPU when the emulated guest timer fired. Commit accb99bcd0ca > > ("KVM: arm/arm64: Simplify bg_timer programming") reworked the timer > > logic to be even more precise, by waiting until the vCPU was actually > > scheduled out, and so move the timer logic from the (un)blocking hooks to > > vcpu_load/put. > > > > In the meantime, the hooks gained usage for enabling vGIC v4 doorbells in > > commit df9ba95993b9 ("KVM: arm/arm64: GICv4: Use the doorbell interrupt > > as an unblocking source"), and added related logic for the VMCR in commit > > 5eeaf10eec39 ("KVM: arm/arm64: Sync ICH_VMCR_EL2 back when about to block"). > > > > Finally, commit 07ab0f8d9a12 ("KVM: Call kvm_arch_vcpu_blocking early > > into the blocking sequence") hoisted the (un)blocking hooks so that they > > wrapped KVM's halt-polling logic in addition to the core "block" logic. > > > > In other words, the original need for arch hooks to take action _only_ > > in the block path is long since gone. > > > > Cc: Oliver Upton <oupton@google.com> > > Cc: Marc Zyngier <maz@kernel.org> > > Signed-off-by: Sean Christopherson <seanjc@google.com> > > This needs a word on why kvm_psci_vcpu_suspend does not need the > hooks. Or it needs to be changed to also use kvm_vcpu_wfi in the PSCI > code, I don't know. > > Marc, can you review and/or advise?
I was looking at that over the weekend, and that's a pre-existing bug. I would have addressed it independently, but it looks like you already have queued the patch.
I guess I'll have to revisit this once the whole thing lands somewhere.
M.
-- Without deviation from the norm, progress is not possible.
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