| Message ID | 20171204200506.3224-3-cdall@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Dec 04, 2017 at 09:05:00PM +0100, Christoffer Dall wrote: > From: Christoffer Dall <christoffer.dall@linaro.org> > > 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. Typo: means? > 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. > > Acked-by: Marc Zyngier <marc.zyngier@arm.com> > Reviewed-by: Andre Przywara <andre.przywara@arm.com> > Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org> > --- > virt/kvm/arm/vgic/vgic-mmio.c | 44 +++++++++++++++++++++++++++---------------- > 1 file changed, 28 insertions(+), 16 deletions(-) > > diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c > index deb51ee16a3d..747b0a3b4784 100644 > --- a/virt/kvm/arm/vgic/vgic-mmio.c > +++ b/virt/kvm/arm/vgic/vgic-mmio.c > @@ -122,6 +122,27 @@ 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 Typo: from within? > + * access. > + * > + * We can disable preemption locally around accessing the per-CPU variable, > + * and use the resolved vcpu pointer after enabling preemption again, 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) > @@ -184,24 +205,10 @@ 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; > unsigned long flags; > - spin_lock_irqsave(&irq->irq_lock, flags); > + 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_irqsave(&irq->irq_lock, flags); > > /* > * If this virtual IRQ was written into a list register, we > @@ -213,6 +220,11 @@ 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 */ > -- > 2.14.2
On Tue, Dec 05, 2017 at 04:46:08PM +0300, Yury Norov wrote: > On Mon, Dec 04, 2017 at 09:05:00PM +0100, Christoffer Dall wrote: > > From: Christoffer Dall <christoffer.dall@linaro.org> > > > > 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. > > Typo: means? > yes > > 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. > > > > Acked-by: Marc Zyngier <marc.zyngier@arm.com> > > Reviewed-by: Andre Przywara <andre.przywara@arm.com> > > Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org> > > --- > > virt/kvm/arm/vgic/vgic-mmio.c | 44 +++++++++++++++++++++++++++---------------- > > 1 file changed, 28 insertions(+), 16 deletions(-) > > > > diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c > > index deb51ee16a3d..747b0a3b4784 100644 > > --- a/virt/kvm/arm/vgic/vgic-mmio.c > > +++ b/virt/kvm/arm/vgic/vgic-mmio.c > > @@ -122,6 +122,27 @@ 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 > > Typo: from within? > yes > > + * access. > > + * > > + * We can disable preemption locally around accessing the per-CPU variable, > > + * and use the resolved vcpu pointer after enabling preemption again, 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) > > @@ -184,24 +205,10 @@ 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; > > unsigned long flags; > > - spin_lock_irqsave(&irq->irq_lock, flags); > > + 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_irqsave(&irq->irq_lock, flags); > > > > /* > > * If this virtual IRQ was written into a list register, we > > @@ -213,6 +220,11 @@ 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 */ > > -- > > 2.14.2 Thanks, -Christoffer
diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c index deb51ee16a3d..747b0a3b4784 100644 --- a/virt/kvm/arm/vgic/vgic-mmio.c +++ b/virt/kvm/arm/vgic/vgic-mmio.c @@ -122,6 +122,27 @@ 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, + * and use the resolved vcpu pointer after enabling preemption again, 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) @@ -184,24 +205,10 @@ 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; unsigned long flags; - spin_lock_irqsave(&irq->irq_lock, flags); + 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_irqsave(&irq->irq_lock, flags); /* * If this virtual IRQ was written into a list register, we @@ -213,6 +220,11 @@ 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 */