On Mon, 25 Oct 2021 14:31:48 +0100,
Paolo Bonzini [off-list ref] wrote:

On 09/10/21 04:12, Sean Christopherson wrote:

quoted

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 <redacted>
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.