Re: [RFC PATCH 09/45] KVM: arm/arm64: vgic-new: Add GICv2 IRQ sync/flush

Christoffer Dall
2016-03-30T13:52:35Z

On Fri, Mar 25, 2016 at 02:04:32AM +0000, Andre Przywara wrote:
> From: Marc Zyngier <marc.zyngier@arm.com>
>
> Implement the functionality for syncing IRQs between our emulation
> and the list registers, which represent the guest's view of IRQs.
> This is done in kvm_vgic_flush_hwstate and kvm_vgic_sync_hwstate,
> which gets called on guest entry and exit.

I thought we agreed to split this up in a generic part and then GICv2
and GICv3 parts following, but ok, I'll look through this code, but I
strongly suggest splitting it up for the next posting.

>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> include/kvm/vgic/vgic.h | 4 +
> virt/kvm/arm/vgic/vgic-v2.c | 161 ++++++++++++++++++++++++++++++++++
> virt/kvm/arm/vgic/vgic.c | 204 ++++++++++++++++++++++++++++++++++++++++++++
> virt/kvm/arm/vgic/vgic.h | 4 +
> 4 files changed, 373 insertions(+)
>
> diff --git a/include/kvm/vgic/vgic.h b/include/kvm/vgic/vgic.h
> index f32b284..986f23f 100644
> --- a/include/kvm/vgic/vgic.h
> +++ b/include/kvm/vgic/vgic.h
> @@ -187,6 +187,10 @@ int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int intid,
> #define vgic_valid_spi(k,i) (((i) >= VGIC_NR_PRIVATE_IRQS) && \
> ((i) < (k)->arch.vgic.nr_spis + VGIC_NR_PRIVATE_IRQS))
>
> +bool kvm_vcpu_has_pending_irqs(struct kvm_vcpu *vcpu);
> +void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu);
> +void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu);
> +
> /**
> * kvm_vgic_get_max_vcpus - Get the maximum number of VCPUs allowed by HW
> *
> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
> index 0bf6f27..1cec423 100644
> --- a/virt/kvm/arm/vgic/vgic-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-v2.c
> @@ -14,11 +14,172 @@
> * along with this program. If not, see <http://www.gnu.org/licenses/>.
> */
>
> +#include <linux/irqchip/arm-gic.h>
> #include <linux/kvm.h>
> #include <linux/kvm_host.h>
>
> #include "vgic.h"
>
> +/*
> + * Call this function to convert a u64 value to an unsigned long * bitmask
> + * in a way that works on both 32-bit and 64-bit LE and BE platforms.
> + *
> + * Warning: Calling this function may modify *val.
> + */
> +static unsigned long *u64_to_bitmask(u64 *val)
> +{
> +#if defined(CONFIG_CPU_BIG_ENDIAN) && BITS_PER_LONG == 32
> + *val = (*val >> 32) | (*val << 32);
> +#endif
> + return (unsigned long *)val;
> +}
> +
> +void vgic_v2_process_maintenance(struct kvm_vcpu *vcpu)
> +{
> + struct vgic_v2_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v2;
> +
> + if (cpuif->vgic_misr & GICH_MISR_EOI) {
> + u64 eisr = cpuif->vgic_eisr;
> + unsigned long *eisr_bmap = u64_to_bitmask(&eisr);
> + int lr;
> +
> + for_each_set_bit(lr, eisr_bmap, vcpu->arch.vgic_cpu.nr_lr) {
> + struct vgic_irq *irq;
> + u32 intid = cpuif->vgic_lr[lr] & GICH_LR_VIRTUALID;
> +
> + irq = vgic_get_irq(vcpu->kvm, vcpu, intid);
> +
> + WARN_ON(irq->config == VGIC_CONFIG_EDGE);
> + WARN_ON(cpuif->vgic_lr[lr] & GICH_LR_STATE);
> +
> + kvm_notify_acked_irq(vcpu->kvm, 0,
> + intid - VGIC_NR_PRIVATE_IRQS);
> +
> + cpuif->vgic_lr[lr] &= ~GICH_LR_STATE; /* Useful?? */

we just had a warning above if the LR state was set, so how do we
expect this to be modified in the mean time?

The following line caters for the famous hardware race, right? If so, I think it deserved a comment:

/*
* The hardware doesn't guarantee that the LR's bit is set in the ELRSR
* despite the virtual interrupt being EOIed and generating a
* maintenance interrupt. Force the bit to be set.
*/

> + cpuif->vgic_elrsr |= 1ULL << lr;
> + }
> + }
> +
> + /* check and disable underflow maintenance IRQ */

s/check and d/D/

> + cpuif->vgic_hcr &= ~GICH_HCR_UIE;

I think the above should be moved to fold_lr_state

> +
> + /*
> + * In the next iterations of the vcpu loop, if we sync the
> + * vgic state after flushing it, but before entering the guest
> + * (this happens for pending signals and vmid rollovers), then
> + * make sure we don't pick up any old maintenance interrupts
> + * here.
> + */
> + cpuif->vgic_eisr = 0;
> +}
> +
> +void vgic_v2_set_underflow(struct kvm_vcpu *vcpu)
> +{
> + struct vgic_v2_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v2;
> +
> + cpuif->vgic_hcr |= GICH_HCR_UIE;
> +}
> +
> +/*
> + * transfer the content of the LRs back into the corresponding ap_list:
> + * - active bit is transferred as is
> + * - pending bit is
> + * - transferred as is in case of edge sensitive IRQs
> + * - set to the line-level (resample time) for level sensitive IRQs
> + */
> +void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu)
> +{
> + struct vgic_v2_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v2;
> + int lr;
> +
> + for (lr = 0; lr < vcpu->arch.vgic_cpu.used_lrs; lr++) {
> + u32 val = cpuif->vgic_lr[lr];
> + u32 intid = val & GICH_LR_VIRTUALID;
> + struct vgic_irq *irq;
> +
> + irq = vgic_get_irq(vcpu->kvm, vcpu, intid);
> +
> + spin_lock(&irq->irq_lock);
> +
> + /* Always preserve the active bit */
> + irq->active = !!(val & GICH_LR_ACTIVE_BIT);
> +
> + /* Edge is the only case where we preserve the pending bit */
> + if (irq->config == VGIC_CONFIG_EDGE &&
> + (val & GICH_LR_PENDING_BIT)) {
> + irq->pending = true;
> +
> + if (intid < VGIC_NR_SGIS) {
> + u32 cpuid = val & GICH_LR_PHYSID_CPUID;
> +
> + cpuid >>= GICH_LR_PHYSID_CPUID_SHIFT;

Are we happy with relying on all the remaining bits being 0 here or
should we define a proper CPUID mask?

> + irq->source |= (1 << cpuid);
> + }
> + }
> +
> + /* Clear soft pending state when level IRQs have been acked */
> + if (irq->config == VGIC_CONFIG_LEVEL &&
> + !(val & GICH_LR_PENDING_BIT)) {
> + irq->soft_pending = false;
> + irq->pending = irq->line_level;
> + }
> +
> + spin_unlock(&irq->irq_lock);
> + }
> +}
> +
> +/*
> + * Populates the particular LR with the state of a given IRQ:
> + * - for an edge sensitive IRQ the pending state is reset in the struct

s/reset/cleared/
s/the struct/the vgic_irq struct/

> + * - for a level sensitive IRQ the pending state value is unchanged;
> + * it will be resampled on deactivation

s/
it will be resampled on deactivation/
it is dictated directly by the input level/

> + *
> + * If irq is not NULL, the irq_lock must be hold already by the caller.

s/hold/held/

> + * If irq is NULL, the respective LR gets cleared.

If @irq describes an SGI with multiple sources, we choose the
lowest-numbered source VCPU and clear that bit in the source bitmap.

> + */
> +void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr)
> +{
> + u32 val;
> +
> + if (!irq) {
> + val = 0;
> + goto out;
> + }

I'm not convinced about keeping this functionality in this function.

Wouldn't it be much more clear to have vgic_clear_lr() as a separate
function?

> +
> + val = irq->intid;
> +
> + if (irq->pending) {
> + val |= GICH_LR_PENDING_BIT;
> +
> + if (irq->config == VGIC_CONFIG_EDGE)
> + irq->pending = false;
> +
> + if (irq->intid < VGIC_NR_SGIS) {
> + u32 src = ffs(irq->source);

can't you do src = __ffs(irq->source) here to avoid the (src - 1) below?

> +
> + BUG_ON(!src);
> + val |= (src - 1) << GICH_LR_PHYSID_CPUID_SHIFT;
> + irq->source &= ~(1 << (src - 1));
> + if (irq->source)
> + irq->pending = true;
> + }
> + }
> +
> + if (irq->active)
> + val |= GICH_LR_ACTIVE_BIT;
> +
> + if (irq->hw) {
> + val |= GICH_LR_HW;
> + val |= irq->hwintid << GICH_LR_PHYSID_CPUID_SHIFT;
> + } else {
> + if (irq->config == VGIC_CONFIG_LEVEL)
> + val |= GICH_LR_EOI;
> + }
> +
> +out:
> + vcpu->arch.vgic_cpu.vgic_v2.vgic_lr[lr] = val;
> +}
> +
> void vgic_v2_irq_change_affinity(struct kvm *kvm, u32 intid, u8 new_targets)
> {
> struct vgic_dist *dist = &kvm->arch.vgic;
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 29c753e..90a85bf 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -273,3 +273,207 @@ int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int intid,
> vgic_update_irq_pending(kvm, vcpu, intid, level);
> return 0;
> }
> +
> +/**
> + * vgic_prune_ap_list - Remove non-relevant interrupts from the list
> + *
> + * @vcpu: The VCPU pointer
> + *
> + * Go over the list of "interesting" interrupts, and prune those that we
> + * won't have to consider in the near future.
> + */
> +static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
> +{
> + struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> + struct vgic_irq *irq, *tmp;
> +
> +retry:
> + spin_lock(&vgic_cpu->ap_list_lock);
> +
> + list_for_each_entry_safe(irq, tmp, &vgic_cpu->ap_list_head, ap_list) {
> + struct kvm_vcpu *target_vcpu, *vcpuA, *vcpuB;
> +
> + spin_lock(&irq->irq_lock);
> +
> + BUG_ON(vcpu != irq->vcpu);
> +
> + target_vcpu = vgic_target_oracle(irq);
> +
> + if (!target_vcpu) {
> + /*
> + * We don't need to process this interrupt any
> + * further, move it off the list.
> + */
> + list_del_init(&irq->ap_list);

why list_del_init and not list_del here? do we ever do list_empty() on
the &irq->ap_list ?

> + irq->vcpu = NULL;
> + spin_unlock(&irq->irq_lock);
> + continue;
> + }
> +
> + if (target_vcpu == vcpu) {
> + /* We're on the right CPU */
> + spin_unlock(&irq->irq_lock);
> + continue;
> + }
> +
> + /* This interrupt looks like it has to be migrated. */
> +
> + spin_unlock(&irq->irq_lock);
> + spin_unlock(&vgic_cpu->ap_list_lock);
> +
> + /*
> + * Ensure locking order by always locking the smallest
> + * ID first.
> + */
> + if (vcpu->vcpu_id < target_vcpu->vcpu_id) {
> + vcpuA = vcpu;
> + vcpuB = target_vcpu;
> + } else {
> + vcpuA = target_vcpu;
> + vcpuB = vcpu;
> + }
> +
> + spin_lock(&vcpuA->arch.vgic_cpu.ap_list_lock);
> + spin_lock(&vcpuB->arch.vgic_cpu.ap_list_lock);
> + spin_lock(&irq->irq_lock);
> +
> + /*
> + * If the affinity has been preserved, move the
> + * interrupt around. Otherwise, it means things have
> + * changed while the interrupt was unlocked, and we
> + * need to replay this.
> + *
> + * In all cases, we cannot trust the list not to have
> + * changed, so we restart from the beginning.
> + */
> + if (target_vcpu == vgic_target_oracle(irq)) {
> + struct vgic_cpu *new_cpu = &target_vcpu->arch.vgic_cpu;
> +
> + list_del_init(&irq->ap_list);

again, why list_del_init and not just list_del ?

> + irq->vcpu = target_vcpu;
> + list_add_tail(&irq->ap_list, &new_cpu->ap_list_head);
> + }
> +
> + spin_unlock(&irq->irq_lock);
> + spin_unlock(&vcpuB->arch.vgic_cpu.ap_list_lock);
> + spin_unlock(&vcpuA->arch.vgic_cpu.ap_list_lock);
> + goto retry;
> + }
> +
> + spin_unlock(&vgic_cpu->ap_list_lock);
> +}
> +
> +static inline void vgic_process_maintenance_interrupt(struct kvm_vcpu *vcpu)
> +{
> + if (kvm_vgic_global_state.type == VGIC_V2)
> + vgic_v2_process_maintenance(vcpu);
> + else
> + WARN(1, "GICv3 Not Implemented\n");
> +}
> +
> +static inline void vgic_fold_lr_state(struct kvm_vcpu *vcpu)
> +{
> + if (kvm_vgic_global_state.type == VGIC_V2)
> + vgic_v2_fold_lr_state(vcpu);
> + else
> + WARN(1, "GICv3 Not Implemented\n");
> +}
> +
> +/*
> + * Requires the ap_lock to be held.
> + * If irq is not NULL, requires the IRQ lock to be held as well.
> + * If irq is NULL, the list register gets cleared.
> + */
> +static inline void vgic_populate_lr(struct kvm_vcpu *vcpu,
> + struct vgic_irq *irq, int lr)
> +{
> + if (kvm_vgic_global_state.type == VGIC_V2)
> + vgic_v2_populate_lr(vcpu, irq, lr);
> + else
> + WARN(1, "GICv3 Not Implemented\n");
> +}
> +
> +static inline void vgic_set_underflow(struct kvm_vcpu *vcpu)
> +{
> + if (kvm_vgic_global_state.type == VGIC_V2)
> + vgic_v2_set_underflow(vcpu);
> + else
> + WARN(1, "GICv3 Not Implemented\n");
> +}
> +
> +static int compute_ap_list_depth(struct kvm_vcpu *vcpu)
> +{
> + struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> + struct vgic_irq *irq;
> + int count = 0;
> +
> + list_for_each_entry(irq, &vgic_cpu->ap_list_head, ap_list) {
> + spin_lock(&irq->irq_lock);
> + /* GICv2 SGIs can count for more than one... */
> + if (irq->intid < VGIC_NR_SGIS && irq->source)

how can we have an SGI on an AP list without the irq->source field set?

Is the irq->source check to cater for GICv3?

> + count += hweight8(irq->source);
> + else
> + count++;
> + spin_unlock(&irq->irq_lock);
> + }
> + return count;

this does feel like an awful lot of code on each entry. I'm wondering
if we should have a count on each vgic_cpu containing the length of the
AP list which is then adjusted via the queue and removal functions?

> +}
> +
> +/* requires the vcpu ap_lock to be held */

s/ap_lock/ap_list_lock/

> +static void vgic_populate_lrs(struct kvm_vcpu *vcpu)

I'm not in love with the fact that we have two separate functions named:

vgic_populate_lrs and
vgic_populate_lr

perhaps this could be changed to 'vgic_flush_ap_list' ?

> +{
> + struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> + u32 model = vcpu->kvm->arch.vgic.vgic_model;
> + struct vgic_irq *irq;
> + int count = 0;
> +
> + if (compute_ap_list_depth(vcpu) > vcpu->arch.vgic_cpu.nr_lr) {
> + vgic_set_underflow(vcpu);
> + vgic_sort_ap_list(vcpu);
> + }
> +
> + list_for_each_entry(irq, &vgic_cpu->ap_list_head, ap_list) {
> + spin_lock(&irq->irq_lock);
> +
> + if (unlikely(vgic_target_oracle(irq) != vcpu))
> + goto next;
> +
> + /*
> + * If we get an SGI with multiple sources, try to get
> + * them in all at once.
> + */
> + if (model == KVM_DEV_TYPE_ARM_VGIC_V2 &&
> + irq->intid < VGIC_NR_SGIS) {

I wonder if a lot of this code would be more readable if we added and
used the following primitives:
vgic_irq_is_sgi()
vgic_irq_is_ppi()
vgic_irq_is_spi()

> + while (irq->source && count < vcpu->arch.vgic_cpu.nr_lr)
> + vgic_populate_lr(vcpu, irq, count++);
> + } else {
> + vgic_populate_lr(vcpu, irq, count++);
> + }

this stuff about the SGIs is really dense, so I'm wondering if it's more
clean to make it even more dense and rewrite the whole if-statement to:

do {
vgic_populate(vcpu, irq, count++);
} while (irq->source && count < vgic.nr_lr);

(btw. I believe all these places referencing the nr_lr in the vgic_cpu
struct could use the global state structure instead).

> +
> +next:
> + spin_unlock(&irq->irq_lock);
> +
> + if (count == vcpu->arch.vgic_cpu.nr_lr)
> + break;
> + }
> +
> + vcpu->arch.vgic_cpu.used_lrs = count;
> +
> + /* Nuke remaining LRs */
> + for ( ; count < vcpu->arch.vgic_cpu.nr_lr; count++)
> + vgic_populate_lr(vcpu, NULL, count);

should we not change this to adhere to the optimizations Marc
implemented for the current VGIC (i.e. clear the LRs on sync+init, and
only write what you need here)?

> +}
> +
> +void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
> +{
> + vgic_process_maintenance_interrupt(vcpu);
> + vgic_fold_lr_state(vcpu);
> + vgic_prune_ap_list(vcpu);
> +}
> +
> +void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
> +{
> + spin_lock(&vcpu->arch.vgic_cpu.ap_list_lock);
> + vgic_populate_lrs(vcpu);
> + spin_unlock(&vcpu->arch.vgic_cpu.ap_list_lock);
> +}
> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
> index b2faf00..95ef3cf 100644
> --- a/virt/kvm/arm/vgic/vgic.h
> +++ b/virt/kvm/arm/vgic/vgic.h
> @@ -21,5 +21,9 @@ struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
> bool vgic_queue_irq(struct kvm *kvm, struct vgic_irq *irq);
>
> void vgic_v2_irq_change_affinity(struct kvm *kvm, u32 intid, u8 target);
> +void vgic_v2_process_maintenance(struct kvm_vcpu *vcpu);
> +void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu);
> +void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr);
> +void vgic_v2_set_underflow(struct kvm_vcpu *vcpu);
>
> #endif
> --
> 2.7.3
>

Thanks,
-Christoffer