From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4AC2D472F7C; Tue, 18 Aug 2026 13:24:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787059484; cv=none; b=kjCa+UOhgX12kOGlry9uVE3wTCkgkPYBm2NWIC550pD/PzQNWBZEg4v0kfUkOzRQXQZ3JQVQJd9M4HMQMnoawANwfjaY/S2jg/ZKAOl68FcLIWPwjta8y0TaaFuMStAp19d2bFUNOI6DIW0IPFjgHLJ3uk9bEaA3PnP1xXYSCRM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787059484; c=relaxed/simple; bh=0qeab45JSjlGLR/DCB210viV8qlg/swbTJ0ATdhPMMQ=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=UpgATd7Vz2CCzX5fCavsNgm+dd0ekdwFRJx/sgDzdLCWwNWWJV3renoIL6JnZpZNDO60v/1kP2zi5mGVBTxXTLPkU8yyFrvU3ugX7uGmC/uVtw05N1dMIhs2VT+x8LlyV8epi1RiyBR1+kd+nWNDBkbRMyGOVrleZs9B3eeQs8U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IvVZYmEa; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IvVZYmEa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B35DA1F000E9; Tue, 18 Aug 2026 13:24:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787059480; bh=S9IekfwPh1alq+9HUJBgkgWBggDNvqQ7KorXgNc8Ifs=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=IvVZYmEaJduqxhOqhcvQD6aUJ5moa6wleRg5iMNiAoqHR0kpyRYwkcmV8O1leHavm tHo0yzgUIPTgyAIVpWqsHXNG9EZFb4zHvmqhzqdt5beIrh5RM9ApemL/khZQ1K8R3L f2sOHxoQQU2gaX4cHv6EOcE8V3UvV6H8c/Kzruipq837mNNP4eoeqz3ijsfX0Hnz7t y0j8Ezkj9DAraCHbOofWu3l3nZQFIrdZCasEitIvw624qqSDw8HnFmRZzK8H2KsOfY ZzcTZ22iR7zh9TCiBnPo1jrzRK68HOpCUxOkDPLC06dwACN5kBeUUICKJ9XIFofHVb cybyTXnvLyBhA== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wwJny-0000000Gdt3-10V2; Tue, 18 Aug 2026 13:24:38 +0000 Date: Tue, 18 Aug 2026 14:24:37 +0100 Message-ID: <86cxvf5zoq.wl-maz@kernel.org> From: Marc Zyngier To: Dongli Zhang Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, oupton@kernel.org, fuad.tabba@linux.dev, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, dwmw2@infradead.org, joe.jin@oracle.com Subject: Re: [PATCH 2/4] KVM: arm64: Reset last_steal on vCPU pid change In-Reply-To: <77baeb6c-1efa-45fb-8a86-46a6c76b5873@oracle.com> References: <20260816053630.527528-1-dongli.zhang@oracle.com> <20260816053630.527528-3-dongli.zhang@oracle.com> <86se4dyw7n.wl-maz@kernel.org> <77baeb6c-1efa-45fb-8a86-46a6c76b5873@oracle.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: dongli.zhang@oracle.com, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, oupton@kernel.org, fuad.tabba@linux.dev, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, dwmw2@infradead.org, joe.jin@oracle.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Mon, 17 Aug 2026 22:29:22 +0100, Dongli Zhang wrote: > > > > On Mon, Aug 17, 2026 1:42:20AM -0700, Marc Zyngier wrote: > > On Sun, 16 Aug 2026 06:33:03 +0100, > > Dongli Zhang wrote: [...] > >> diff --git a/arch/arm64/kvm/pvtime.c b/arch/arm64/kvm/pvtime.c > >> index 4ceabaa4c30b..000bf49cc0fd 100644 > >> --- a/arch/arm64/kvm/pvtime.c > >> +++ b/arch/arm64/kvm/pvtime.c > >> @@ -32,6 +32,11 @@ void kvm_update_stolen_time(struct kvm_vcpu *vcpu) > >> srcu_read_unlock(&kvm->srcu, idx); > >> } > >> > >> +void kvm_reset_stolen_time(struct kvm_vcpu *vcpu) > >> +{ > >> + vcpu->arch.steal.last_steal = current->sched_info.run_delay; > >> +} > >> + > >> long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu) > >> { > >> u32 feature = smccc_get_arg1(vcpu); > > > > Why isn't this common code? I really don't see the point in making > > this arch-specific code. I'd expect something like this (untested): > > > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > > index ace5801a592f..3fb77360af01 100644 > > --- a/arch/arm64/include/asm/kvm_host.h > > +++ b/arch/arm64/include/asm/kvm_host.h > > @@ -950,6 +950,8 @@ struct kvm_vcpu_arch { > > pid_t pid; > > }; > > > > +#define kvm_arch_vcpu_last_steal(v) (v)->arch.steal.last_steal > > + > > /* > > * Each 'flag' is composed of a comma-separated triplet: > > * > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 45e784462ec6..117aeb49231a 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -4459,6 +4459,9 @@ static long kvm_vcpu_ioctl(struct file *filp, > > if (r) > > break; > > > > + if (IS_ENABLED(CONFIG_HAVE_PV_STEAL_CLOCK_GEN)) > > + kvm_arch_vcpu_last_steal(vcpu) = current->sched_info.run_delay; > > + > > newpid = get_task_pid(current, PIDTYPE_PID); > > write_lock(&vcpu->pid_lock); > > vcpu->pid = newpid; > > > > where each architecture that implements steal time provides an > > accessor, and the core code is in charge of the adjustment. > > > > It also makes sure that we don't leave any architecture behind. > > > Or how about making it something like below? > > if (IS_ENABLED(CONFIG_HAVE_PV_STEAL_CLOCK_GEN)) > kvm_arch_vcpu_reset_last_steal(vcpu); > > That would still move the policy to common KVM code, while leaving the exact > arch state to the architecture implementation. I don't think architectures should have a say in this. Steal time, as a PV service, should not involve the architectures at all. After all, that's the whole point of a PV service: hypervisor-specific hacks that do not fit in the architectural envelope. Bonus points if you move the last_steal field in the main vcpu structure instead of some arch-specific one. > For x86, the hook can reset vcpu->arch.st.last_steal for regular KVM steal time. > If we also decide to cover Xen runstate in this series, the same x86 hook can > additionally reset vcpu->arch.xen.last_steal. For arch-specific stuff, there is the pid change hook already. M. -- Without deviation from the norm, progress is not possible.