From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH v4 2/7] KVM: arm/arm64: Factor out functionality to get vgic mmio requester_vcpu Date: Tue, 10 Oct 2017 11:27:44 +0100 Message-ID: <87o9pfuwkf.fsf@on-the-bus.cambridge.arm.com> References: <1505513994-77939-1-git-send-email-christoffer.dall@linaro.org> <1505513994-77939-3-git-send-email-christoffer.dall@linaro.org> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <1505513994-77939-3-git-send-email-christoffer.dall@linaro.org> (Christoffer Dall's message of "Fri, 15 Sep 2017 15:19:49 -0700") Sender: kvm-owner@vger.kernel.org To: Christoffer Dall Cc: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Eric Auger , kvm@vger.kernel.org, Christoffer Dall List-Id: kvmarm@lists.cs.columbia.edu On Fri, Sep 15 2017 at 3:19:49 pm BST, Christoffer Dall wrote: > From: Christoffer Dall > > We are about to distinguish between userspace accesses and mmio traps > for a number of the mmio handlers. When the requester vcpu is NULL, it > mens we are handling a userspace acccess. > > Factor out the functionality to get the request vcpu into its own > function, mostly so we have a common place to document the semantics of > the return value. > > Also take the chance to move the functionality outside of holding a > spinlock and instead explicitly disable and enable preemption. This > supports PREEMPT_RT kernels as well. > > Signed-off-by: Christoffer Dall > --- > virt/kvm/arm/vgic/vgic-mmio.c | 43 +++++++++++++++++++++++++++---------------- > 1 file changed, 27 insertions(+), 16 deletions(-) > > diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c > index c1e4bdd..f3087f6 100644 > --- a/virt/kvm/arm/vgic/vgic-mmio.c > +++ b/virt/kvm/arm/vgic/vgic-mmio.c > @@ -120,6 +120,26 @@ unsigned long vgic_mmio_read_pending(struct kvm_vcpu *vcpu, > return value; > } > > +/* > + * This function will return the VCPU that performed the MMIO access and > + * trapped from twithin the VM, and will return NULL if this is a userspace > + * access. > + * > + * We can disable preemption locally around accessing the per-CPU variable > + * because even if the current thread is migrated to another CPU, reading the > + * per-CPU value later will give us the same value as we update the per-CPU > + * variable in the preempt notifier handlers. > + */ > +static struct kvm_vcpu *vgic_get_mmio_requester_vcpu(void) > +{ > + struct kvm_vcpu *vcpu; > + > + preempt_disable(); > + vcpu = kvm_arm_get_running_vcpu(); > + preempt_enable(); > + return vcpu; > +} > + > void vgic_mmio_write_spending(struct kvm_vcpu *vcpu, > gpa_t addr, unsigned int len, > unsigned long val) > @@ -180,23 +200,9 @@ unsigned long vgic_mmio_read_active(struct kvm_vcpu *vcpu, > static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq, > bool new_active_state) > { > - struct kvm_vcpu *requester_vcpu; > - spin_lock(&irq->irq_lock); > + struct kvm_vcpu *requester_vcpu = vgic_get_mmio_requester_vcpu(); > > - /* > - * The vcpu parameter here can mean multiple things depending on how > - * this function is called; when handling a trap from the kernel it > - * depends on the GIC version, and these functions are also called as > - * part of save/restore from userspace. > - * > - * Therefore, we have to figure out the requester in a reliable way. > - * > - * When accessing VGIC state from user space, the requester_vcpu is > - * NULL, which is fine, because we guarantee that no VCPUs are running > - * when accessing VGIC state from user space so irq->vcpu->cpu is > - * always -1. > - */ > - requester_vcpu = kvm_arm_get_running_vcpu(); > + spin_lock(&irq->irq_lock); > > /* > * If this virtual IRQ was written into a list register, we > @@ -208,6 +214,11 @@ static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq, > * vgic_change_active_prepare) and still has to sync back this IRQ, > * so we release and re-acquire the spin_lock to let the other thread > * sync back the IRQ. > + * > + * When accessing VGIC state from user space, requester_vcpu is > + * NULL, which is fine, because we guarantee that no VCPUs are running > + * when accessing VGIC state from user space so irq->vcpu->cpu is > + * always -1. > */ > while (irq->vcpu && /* IRQ may have state in an LR somewhere */ > irq->vcpu != requester_vcpu && /* Current thread is not the VCPU thread */ Acked-by: Marc Zyngier M. -- Jazz is not dead, it just smell funny.