From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex =?utf-8?Q?Benn=C3=A9e?= Subject: Re: [PATCH v10 04/18] KVM: arm/arm64: Introduce kvm_arch_vcpu_run_pid_change Date: Wed, 23 May 2018 15:34:20 +0100 Message-ID: <87muwqtp8z.fsf@linaro.org> References: <1527005119-6842-1-git-send-email-Dave.Martin@arm.com> <1527005119-6842-5-git-send-email-Dave.Martin@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 8017B4A0CC for ; Wed, 23 May 2018 10:24:05 -0400 (EDT) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id BKCUGYfjJaQi for ; Wed, 23 May 2018 10:23:43 -0400 (EDT) Received: from mail-wr0-f194.google.com (mail-wr0-f194.google.com [209.85.128.194]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id A2E7A49F8C for ; Wed, 23 May 2018 10:23:43 -0400 (EDT) Received: by mail-wr0-f194.google.com with SMTP id i14-v6so26939615wre.2 for ; Wed, 23 May 2018 07:34:22 -0700 (PDT) In-reply-to: <1527005119-6842-5-git-send-email-Dave.Martin@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: Dave Martin Cc: Christoffer Dall , Ard Biesheuvel , Marc Zyngier , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, Christoffer Dall List-Id: kvmarm@lists.cs.columbia.edu CkRhdmUgTWFydGluIDxEYXZlLk1hcnRpbkBhcm0uY29tPiB3cml0ZXM6Cgo+IEZyb206IENocmlz dG9mZmVyIERhbGwgPGNocmlzdG9mZmVyLmRhbGxAbGluYXJvLm9yZz4KPgo+IEtWTS9BUk0gZGlm ZmVycyBmcm9tIG90aGVyIGFyY2hpdGVjdHVyZXMgaW4gaGF2aW5nIHRvIG1haW50YWluIGFuCj4g YWRkaXRpb25hbCB2aXJ0dWFsIGFkZHJlc3Mgc3BhY2UgZnJvbSB0aGF0IG9mIHRoZSBob3N0IGFu ZCB0aGUKPiBndWVzdCwgYmVjYXVzZSB3ZSBzcGxpdCB0aGUgZXhlY3V0aW9uIG9mIEtWTSBhY3Jv 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an > additional virtual address space from that of the host and the > guest, because we split the execution of KVM across both EL1 and > EL2. > > This results in a need to explicitly map data structures into EL2 > (hyp) which are accessed from the hyp code. As we are about to be > more clever with our FPSIMD handling on arm64, which stores data in > the task struct and uses thread_info flags, we will have to map > parts of the currently executing task struct into the EL2 virtual > address space. > > However, we don't want to do this on every KVM_RUN, because it is a > fairly expensive operation to walk the page tables, and the common > execution mode is to map a single thread to a VCPU. By introducing > a hook that architectures can select with > HAVE_KVM_VCPU_RUN_PID_CHANGE, we do not introduce overhead for > other architectures, but have a simple way to only map the data we > need when required for arm64. > > This patch introduces the framework only, and wires it up in the > arm/arm64 KVM common code. > > No functional change. > > Signed-off-by: Christoffer Dall > Signed-off-by: Dave Martin > Reviewed-by: Marc Zyngier > --- > include/linux/kvm_host.h | 9 +++++++++ > virt/kvm/Kconfig | 3 +++ > virt/kvm/kvm_main.c | 7 ++++++- > 3 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 6930c63..4268ace 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -1276,4 +1276,13 @@ static inline long kvm_arch_vcpu_async_ioctl(struct file *filp, > void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm, > unsigned long start, unsigned long end); > > +#ifdef CONFIG_HAVE_KVM_VCPU_RUN_PID_CHANGE > +int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu); > +#else > +static inline int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu) > +{ > + return 0; > +} > +#endif /* CONFIG_HAVE_KVM_VCPU_RUN_PID_CHANGE */ > + > #endif > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig > index cca7e06..72143cf 100644 > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -54,3 +54,6 @@ config HAVE_KVM_IRQ_BYPASS > > config HAVE_KVM_VCPU_ASYNC_IOCTL > bool > + > +config HAVE_KVM_VCPU_RUN_PID_CHANGE > + bool This almost threw me as I thought you might be able to enable this and break the build, but apparently not: Reviewed-by: Alex Benn?e > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index c7b2e92..c32e240 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -2550,8 +2550,13 @@ static long kvm_vcpu_ioctl(struct file *filp, > oldpid = rcu_access_pointer(vcpu->pid); > if (unlikely(oldpid != current->pids[PIDTYPE_PID].pid)) { > /* The thread running this VCPU changed. */ > - struct pid *newpid = get_task_pid(current, PIDTYPE_PID); > + struct pid *newpid; > > + r = kvm_arch_vcpu_run_pid_change(vcpu); > + if (r) > + break; > + > + newpid = get_task_pid(current, PIDTYPE_PID); > rcu_assign_pointer(vcpu->pid, newpid); > if (oldpid) > synchronize_rcu(); -- Alex Benn?e