Message-ID: <54BD1DD8.7010700@linaro.org>
Date:	Mon, 19 Jan 2015 16:08:08 +0100
From:	Eric Auger <eric.auger@...aro.org>
To:	André Przywara <andre.przywara@....com>,
	eric.auger@...com, christoffer.dall@...aro.org,
	marc.zyngier@....com, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
	alex.williamson@...hat.com, agraf@...e.de, gleb@...nel.org,
	pbonzini@...hat.com, borntraeger@...ibm.com,
	cornelia.huck@...ibm.com
CC:	will.deacon@....com, linux-kernel@...r.kernel.org,
	patches@...aro.org
Subject: Re: [PATCH v7 4/4] KVM: arm/arm64: add irqfd support

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@...aro.org>
>>> Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
>>>
>>> ---
>>>
>>> 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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