Re: [PATCH v7 4/4] KVM: arm/arm64: add irqfd support

From: Eric Auger
Date: Mon Jan 19 2015 - 10:09:57 EST

On 01/19/2015 04:01 PM, Eric Auger wrote:
> Hi Andre,
> On 01/16/2015 11:07 AM, André Przywara wrote:
>> Hi Eric,
>>
>> On 01/15/2015 02:47 PM, Eric Auger wrote:
>>> This patch enables irqfd on arm/arm64.
>>>
>>> Both irqfd and resamplefd are supported. Injection is implemented
>>> in vgic.c without routing.
>>>
>>> This patch enables CONFIG_HAVE_KVM_EVENTFD and CONFIG_HAVE_KVM_IRQFD.
>>>
>>> KVM_CAP_IRQFD is now advertised. KVM_CAP_IRQFD_RESAMPLE capability
>>> automatically is advertised as soon as CONFIG_HAVE_KVM_IRQFD is set.
>>>
>>> Irqfd injection is restricted to SPI. The rationale behind not
>>> supporting PPI irqfd injection is that any device using a PPI would
>>> be a private-to-the-CPU device (timer for instance), so its state
>>> would have to be context-switched along with the VCPU and would
>>> require in-kernel wiring anyhow. It is not a relevant use case for
>>> irqfds.
>>>
>>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
>>> Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>>>
>>> ---
>>>
>>> v5 -> v6:
>>> - KVM_CAP_IRQFD support depends on vgic_present
>>> - add Christoffer's Reviewed-by
>>>
>>> v4 -> v5:
>>> - squash [PATCH v4 3/3] KVM: arm64: add irqfd support into this patch
>>> - some rewording in Documentation/virtual/kvm/api.txt and in vgic
>>> vgic_process_maintenance unlock comment.
>>> - move explanation of why not supporting PPI into commit message
>>> - in case of injection before gic readiness, -ENODEV is returned. It is
>>> up to the user space to avoid this situation.
>>>
>>> v3 -> v4:
>>> - reword commit message
>>> - explain why we unlock the distributor before calling kvm_notify_acked_irq
>>> - rename is_assigned_irq into has_notifier
>>> - change EOI and injection kvm_debug format string
>>> - remove error local variable in kvm_set_irq
>>> - Move HAVE_KVM_IRQCHIP unset in a separate patch
>>> - handle case were the irqfd injection is attempted before the vgic is ready.
>>> in such a case the notifier, if any, is called immediatly
>>> - use nr_irqs to test spi is within correct range
>>>
>>> v2 -> v3:
>>> - removal of irq.h from eventfd.c put in a separate patch to increase
>>> visibility
>>> - properly expose KVM_CAP_IRQFD capability in arm.c
>>> - remove CONFIG_HAVE_KVM_IRQCHIP meaningfull only if irq_comm.c is used
>>>
>>> v1 -> v2:
>>> - rebase on 3.17rc1
>>> - move of the dist unlock in process_maintenance
>>> - remove of dist lock in __kvm_vgic_sync_hwstate
>>> - rewording of the commit message (add resamplefd reference)
>>> - remove irq.h
>>> ---
>>> Documentation/virtual/kvm/api.txt | 6 +++-
>>> arch/arm/include/uapi/asm/kvm.h | 3 ++
>>> arch/arm/kvm/Kconfig | 2 ++
>>> arch/arm/kvm/Makefile | 2 +-
>>> arch/arm/kvm/arm.c | 5 ++++
>>> arch/arm64/include/uapi/asm/kvm.h | 3 ++
>>> arch/arm64/kvm/Kconfig | 2 ++
>>> arch/arm64/kvm/Makefile | 2 +-
>>> virt/kvm/arm/vgic.c | 63 ++++++++++++++++++++++++++++++++++++---
>>> 9 files changed, 81 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>>> index 0007fef..5ed8088 100644
>>> --- a/Documentation/virtual/kvm/api.txt
>>> +++ b/Documentation/virtual/kvm/api.txt
>>> @@ -2231,7 +2231,7 @@ into the hash PTE second double word).
>>> 4.75 KVM_IRQFD
>>>
>>> Capability: KVM_CAP_IRQFD
>>> -Architectures: x86 s390
>>> +Architectures: x86 s390 arm arm64
>>> Type: vm ioctl
>>> Parameters: struct kvm_irqfd (in)
>>> Returns: 0 on success, -1 on error
>>> @@ -2257,6 +2257,10 @@ Note that closing the resamplefd is not sufficient to disable the
>>> irqfd. The KVM_IRQFD_FLAG_RESAMPLE is only necessary on assignment
>>> and need not be specified with KVM_IRQFD_FLAG_DEASSIGN.
>>>
>>> +On ARM/ARM64, the gsi field in the kvm_irqfd struct specifies the Shared
>>> +Peripheral Interrupt (SPI) index, such that the GIC interrupt ID is
>>> +given by gsi + 32.
>>> +
>>> 4.76 KVM_PPC_ALLOCATE_HTAB
>>>
>>> Capability: KVM_CAP_PPC_ALLOC_HTAB
>>> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
>>> index 09ee408..77547bb 100644
>>> --- a/arch/arm/include/uapi/asm/kvm.h
>>> +++ b/arch/arm/include/uapi/asm/kvm.h
>>> @@ -196,6 +196,9 @@ struct kvm_arch_memory_slot {
>>> /* Highest supported SPI, from VGIC_NR_IRQS */
>>> #define KVM_ARM_IRQ_GIC_MAX 127
>>>
>>> +/* One single KVM irqchip, ie. the VGIC */
>>> +#define KVM_NR_IRQCHIPS 1
>>> +
>>> /* PSCI interface */
>>> #define KVM_PSCI_FN_BASE 0x95c1ba5e
>>> #define KVM_PSCI_FN(n) (KVM_PSCI_FN_BASE + (n))
>>> diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
>>> index 9f581b1..e519a40 100644
>>> --- a/arch/arm/kvm/Kconfig
>>> +++ b/arch/arm/kvm/Kconfig
>>> @@ -24,6 +24,7 @@ config KVM
>>> select KVM_MMIO
>>> select KVM_ARM_HOST
>>> depends on ARM_VIRT_EXT && ARM_LPAE
>>> + select HAVE_KVM_EVENTFD
>>> ---help---
>>> Support hosting virtualized guest machines. You will also
>>> need to select one or more of the processor modules below.
>>> @@ -55,6 +56,7 @@ config KVM_ARM_MAX_VCPUS
>>> config KVM_ARM_VGIC
>>> bool "KVM support for Virtual GIC"
>>> depends on KVM_ARM_HOST && OF
>>> + select HAVE_KVM_IRQFD
>>> default y
>>> ---help---
>>> Adds support for a hardware assisted, in-kernel GIC emulation.
>>> diff --git a/arch/arm/kvm/Makefile b/arch/arm/kvm/Makefile
>>> index f7057ed..859db09 100644
>>> --- a/arch/arm/kvm/Makefile
>>> +++ b/arch/arm/kvm/Makefile
>>> @@ -15,7 +15,7 @@ AFLAGS_init.o := -Wa,-march=armv7-a$(plus_virt)
>>> AFLAGS_interrupts.o := -Wa,-march=armv7-a$(plus_virt)
>>>
>>> KVM := ../../../virt/kvm
>>> -kvm-arm-y = $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o
>>> +kvm-arm-y = $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o
>>>
>>> obj-y += kvm-arm.o init.o interrupts.o
>>> obj-y += arm.o handle_exit.o guest.o mmu.o emulate.o reset.o
>>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>>> index 9c905b4..8f8c1da 100644
>>> --- a/arch/arm/kvm/arm.c
>>> +++ b/arch/arm/kvm/arm.c
>>> @@ -172,6 +172,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>> case KVM_CAP_IRQCHIP:
>>> r = vgic_present;
>>> break;
>>> +#ifdef CONFIG_HAVE_KVM_IRQFD
>>> + case KVM_CAP_IRQFD:
>>> + r = vgic_present;
>>> + break;
>>> +#endif
>>> case KVM_CAP_DEVICE_CTRL:
>>> case KVM_CAP_USER_MEMORY:
>>> case KVM_CAP_SYNC_MMU:
>>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>>> index 8e38878..1ed4417 100644
>>> --- a/arch/arm64/include/uapi/asm/kvm.h
>>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>>> @@ -182,6 +182,9 @@ struct kvm_arch_memory_slot {
>>> /* Highest supported SPI, from VGIC_NR_IRQS */
>>> #define KVM_ARM_IRQ_GIC_MAX 127
>>>
>>> +/* One single KVM irqchip, ie. the VGIC */
>>> +#define KVM_NR_IRQCHIPS 1
>>> +
>>> /* PSCI interface */
>>> #define KVM_PSCI_FN_BASE 0x95c1ba5e
>>> #define KVM_PSCI_FN(n) (KVM_PSCI_FN_BASE + (n))
>>> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
>>> index 279e1a0..09c25c2 100644
>>> --- a/arch/arm64/kvm/Kconfig
>>> +++ b/arch/arm64/kvm/Kconfig
>>> @@ -26,6 +26,7 @@ config KVM
>>> select KVM_ARM_HOST
>>> select KVM_ARM_VGIC
>>> select KVM_ARM_TIMER
>>> + select HAVE_KVM_EVENTFD
>>> ---help---
>>> Support hosting virtualized guest machines.
>>>
>>> @@ -50,6 +51,7 @@ config KVM_ARM_MAX_VCPUS
>>> config KVM_ARM_VGIC
>>> bool
>>> depends on KVM_ARM_HOST && OF
>>> + select HAVE_KVM_IRQFD
>>> ---help---
>>> Adds support for a hardware assisted, in-kernel GIC emulation.
>>>
>>> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
>>> index 32a0961..2e6b827 100644
>>> --- a/arch/arm64/kvm/Makefile
>>> +++ b/arch/arm64/kvm/Makefile
>>> @@ -11,7 +11,7 @@ ARM=../../../arch/arm/kvm
>>>
>>> obj-$(CONFIG_KVM_ARM_HOST) += kvm.o
>>>
>>> -kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o
>>> +kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o
>>> kvm-$(CONFIG_KVM_ARM_HOST) += $(ARM)/arm.o $(ARM)/mmu.o $(ARM)/mmio.o
>>> kvm-$(CONFIG_KVM_ARM_HOST) += $(ARM)/psci.o $(ARM)/perf.o
>>>
>>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>>> index 03affc7..d1a5c70 100644
>>> --- a/virt/kvm/arm/vgic.c
>>> +++ b/virt/kvm/arm/vgic.c
>>> @@ -1447,7 +1447,10 @@ epilog:
>>> static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>>> {
>>> u32 status = vgic_get_interrupt_status(vcpu);
>>> + struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
>>> bool level_pending = false;
>>> + struct kvm *kvm = vcpu->kvm;
>>> + bool has_notifier;
>>>
>>> kvm_debug("STATUS = %08x\n", status);
>>>
>>> @@ -1464,6 +1467,7 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>>> struct vgic_lr vlr = vgic_get_lr(vcpu, lr);
>>> WARN_ON(vgic_irq_is_edge(vcpu, vlr.irq));
>>>
>>> + spin_lock(&dist->lock);
>>> vgic_irq_clear_queued(vcpu, vlr.irq);
>>> WARN_ON(vlr.state & LR_STATE_MASK);
>>> vlr.state = 0;
>>> @@ -1482,6 +1486,24 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>>> */
>>> vgic_dist_irq_clear_soft_pend(vcpu, vlr.irq);
>>>
>>> + /*
>>> + * kvm_notify_acked_irq calls kvm_set_irq()
>>> + * to reset the IRQ level. Need to release the
>>> + * lock for kvm_set_irq to grab it.
>>> + */
>>> + spin_unlock(&dist->lock);
>>> +
>>> + has_notifier = kvm_irq_has_notifier(kvm, 0,
>>> + vlr.irq - VGIC_NR_PRIVATE_IRQS);
>>> +
>>> + if (has_notifier) {
>>
>> Could that be racy? Can the irqfd be de-assigned meanwhile? Or am I
>> seeing ghosts here? ;-)
> Well actually kvm_irq_has_notifier implements the same loop as
> kvm_notify_acked_irq but instead of calling the irq_acked() function of
> the notifier it returns true. So the check is done twice. I think I can
> simply drop the kvm_irq_has_notifier check.
>
>>
>>> + kvm_debug("Guest EOIed vIRQ %d on CPU %d\n",
>>> + vlr.irq, vcpu->vcpu_id);
>>> + kvm_notify_acked_irq(kvm, 0,
>>> + vlr.irq - VGIC_NR_PRIVATE_IRQS);
>>> + }
>>> + spin_lock(&dist->lock);
>>> +
>>> /* Any additional pending interrupt? */
>>> if (vgic_dist_irq_get_level(vcpu, vlr.irq)) {
>>> vgic_cpu_irq_set(vcpu, vlr.irq);
>>> @@ -1491,6 +1513,8 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>>> vgic_cpu_irq_clear(vcpu, vlr.irq);
>>> }
>>>
>>> + spin_unlock(&dist->lock);
>>> +
>>> /*
>>> * Despite being EOIed, the LR may not have
>>> * been marked as empty.
>>> @@ -1555,14 +1579,10 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
>>>
>>> void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>>> {
>>> - struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
>>> -
>>> if (!irqchip_in_kernel(vcpu->kvm))
>>> return;
>>>
>>> - spin_lock(&dist->lock);
>>> __kvm_vgic_sync_hwstate(vcpu);
>>> - spin_unlock(&dist->lock);
>>> }
>>
>> Given that you drop the coarse grained locking around
>> __kvm_vgic_sync_hwstate(), can you adjust the comment on top of it and
>> either delete it or relax the locking requirement?
> yes I will remove the comment.
>>
>> Have I got this right that most of the locking is not needed as long as
>> we deal only with VCPU specific data structures, as any preemption would
>> not execute code handling this very VCPU again?
> yes this is my understanding
>>
>>
>> Also it would be beneficial to note the change of the locking in the
>> commit message (or even make it a separate patch). That would help
>> possible bisecting.
> I will add in the commit message since it looks difficult to me to
> separate the lock changes from the kvm_notify_acked_irq call addition
well actually I will add a new commit ;-)

Eric
>>
>>>
>>> int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu)
>>> @@ -2481,3 +2501,38 @@ out_free_irq:
>>> free_percpu_irq(vgic->maint_irq, kvm_get_running_vcpus());
>>> return ret;
>>> }
>>> +
>>> +int kvm_irq_map_gsi(struct kvm *kvm,
>>> + struct kvm_kernel_irq_routing_entry *entries,
>>> + int gsi)
>>> +{
>>> + return gsi;
>>> +}
>>> +
>>> +int kvm_irq_map_chip_pin(struct kvm *kvm, unsigned irqchip, unsigned pin)
>>> +{
>>> + return pin;
>>> +}
>>> +
>>> +int kvm_set_irq(struct kvm *kvm, int irq_source_id,
>>> + u32 irq, int level, bool line_status)
>>> +{
>>> + unsigned int spi = irq + VGIC_NR_PRIVATE_IRQS;
>>> +
>>> + kvm_debug("irqfd sets vIRQ %d to %d\n", irq, level);
>>> +
>>> + if (likely(vgic_initialized(kvm))) {
>>
>> Is that really needed? I reckon we can only get here if an irqfd has
>> been assigned, which is guarded already by that initialization check.
> Effectively we can remove it.
>>
>>> + if (spi > kvm->arch.vgic.nr_irqs)
>>
>> I wonder if that check could be done earlier at assignment time. Does
>> that not work because the assignment is generic code and has no notion
>> of the maximum supported IRQ numbers as the VGIC has?
> yes that's the reason.
>
> Many thanks for the review of the whole series.
>
> Best Regards
>
> Eric
>>
>> Cheers,
>> Andre.
>>
>>> + return -EINVAL;
>>> + return kvm_vgic_inject_irq(kvm, 0, spi, level);
>>> + } else
>>> + return -ENODEV;
>>> +}
>>> +
>>> +/* MSI not implemented yet */
>>> +int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
>>> + struct kvm *kvm, int irq_source_id,
>>> + int level, bool line_status)
>>> +{
>>> + return 0;
>>> +}
>>>
>>
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>

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