From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Date: Tue, 26 Oct 2021 15:41:05 +0000 Subject: Re: [PATCH v2 10/43] KVM: arm64: Move vGIC v4 handling for WFI out arch callback hook Message-Id: <875ytjbxpq.wl-maz@kernel.org> List-Id: References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-11-seanjc@google.com> <9236e715-c471-e1c8-6117-6f37b908a6bd@redhat.com> In-Reply-To: <9236e715-c471-e1c8-6117-6f37b908a6bd@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Paolo Bonzini Cc: Sean Christopherson , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , Oliver Upton , Jing Zhang On Mon, 25 Oct 2021 14:31:48 +0100, Paolo Bonzini 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 > > Cc: Marc Zyngier > > Signed-off-by: Sean Christopherson > > 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.