Re: [PATCH v4 2/2] KVM: arm/arm64: Route vtimer events to user space

[Marc Zyngier]

On 22/09/16 13:32, Alexander Graf wrote:
> On 09/20/2016 11:21 AM, Marc Zyngier wrote:
>> On 19/09/16 18:39, Alexander Graf wrote:
>>>
>>> On 19.09.16 16:48, Marc Zyngier wrote:
>>>
> +
> + /*
> +  * So we can just explicitly mask or unmask the IRQ, gaining
> +  * more compatibility with oddball irq controllers.
> +  */
> + if (phys_active)
> + disable_percpu_irq(host_vtimer_irq);
> + else
> + enable_percpu_irq(host_vtimer_irq, 0);
 Since you are now targeting random irqchips (as opposed to a GIC
 specifically), what guarantees that the timer is a per-cpu IRQ?
>>> This is the host interrupt controller - and we're already using percpu
>>> irqs on it :). Also as it happens the RPi has them percpu (anything else
>>> wouldn't make sense...).
>> Not really. The RPi is faking percpu interrupts just to have some level
>> of compatibility with the host arch timer driver. But nonetheless, if
>> you're opening the code to something else than a GIC, then you should
>> check that the interrupt you're getting is percpu.
> 
> This should already be covered by request_percpu_irq() in 
> kvm_timer_hyp_init(), no?

Ah, true. Ignore me, then.

M.
-- 
Jazz is not dead. It just smells funny...
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Re: [PATCH v4 2/2] KVM: arm/arm64: Route vtimer events to user space

[Marc Zyngier]

On 20/09/16 13:22, Alexander Graf wrote:
> On 09/20/2016 12:28 PM, Marc Zyngier wrote:
>> On 20/09/16 11:05, Alexander Graf wrote:
>>> On 09/20/2016 11:39 AM, Marc Zyngier wrote:
 On 20/09/16 10:26, Alexander Graf wrote:
> On 20.09.16 11:21, Marc Zyngier wrote:
>> On 19/09/16 18:39, Alexander Graf wrote:
>>> On 19.09.16 16:48, Marc Zyngier wrote:
 On 19/09/16 12:14, Alexander Graf wrote:
> We have 2 modes for dealing with interrupts in the ARM world. We can 
> either
> handle them all using hardware acceleration through the vgic or we 
> can emulate
> a gic in user space and only drive CPU IRQ pins from there.
>
> Unfortunately, when driving IRQs from user space, we never tell user 
> space
> about timer events that may result in interrupt line state changes, 
> so we
> lose out on timer events if we run with user space gic emulation.
>
> This patch fixes that by routing vtimer expiration events to user 
> space.
> With this patch I can successfully run edk2 and Linux with user space 
> gic
> emulation.
>
> Signed-off-by: Alexander Graf 
>
> ---
>
> v1 -> v2:
>
> - Add back curly brace that got lost
>
> v2 -> v3:
>
> - Split into patch set
>
> v3 -> v4:
>
> - Improve documentation
> ---
>Documentation/virtual/kvm/api.txt |  30 -
>arch/arm/include/asm/kvm_host.h   |   3 +
>arch/arm/kvm/arm.c|  22 ---
>arch/arm64/include/asm/kvm_host.h |   3 +
>include/uapi/linux/kvm.h  |  14 +
>virt/kvm/arm/arch_timer.c | 125 
> +++---
>6 files changed, 155 insertions(+), 42 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/api.txt 
> b/Documentation/virtual/kvm/api.txt
> index 23937e0..1c0bd86 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3202,9 +3202,14 @@ struct kvm_run {
>   /* in */
>   __u8 request_interrupt_window;
>
> -Request that KVM_RUN return when it becomes possible to inject 
> external
> +[x86] Request that KVM_RUN return when it becomes possible to inject 
> external
>interrupts into the guest.  Useful in conjunction with 
> KVM_INTERRUPT.
>
> +[arm*] Bits set to 1 in here mask IRQ lines that would otherwise 
> potentially
> +trigger forever. These lines are available:
> +
> +KVM_IRQWINDOW_VTIMER  -  Masks hw virtual timer irq while in 
> guest
> +
>   __u8 padding1[7];
>
>   /* out */
> @@ -3519,6 +3524,18 @@ Hyper-V SynIC state change. Notification is 
> used to remap SynIC
>event/message pages and to enable/disable SynIC messages/events 
> processing
>in userspace.
>
> + /* KVM_EXIT_ARM_TIMER */
> + struct {
> + __u8 timesource;
> + } arm_timer;
> +
> +Indicates that a timer triggered that user space needs to handle and
> +potentially mask with vcpu->run->request_interrupt_window to allow 
> the
> +guest to proceed. This only happens for timers that got enabled 
> through
> +KVM_CAP_ARM_TIMER. The following time sources are available:
> +
> +KVM_ARM_TIMER_VTIMER  - virtual cpu timer
> +
>   /* Fix the size of the union. */
>   char padding[256];
>   };
> @@ -3739,6 +3756,17 @@ Once this is done the KVM_REG_MIPS_VEC_* and 
> KVM_REG_MIPS_MSA_* registers can be
>accessed, and the Config5.MSAEn bit is accessible via the KVM API 
> and also from
>the guest.
>
> +6.11 KVM_CAP_ARM_TIMER
> +
> +Architectures: arm, arm64
> +Target: vcpu
> +Parameters: args[0] contains a bitmap of timers to select (see 5.)
> +
> +This capability allows to route per-core timers into user space. 
> When it's
> +enabled and no in-kernel interrupt controller is in use, the timers 
> selected
> +by args[0] trigger KVM_EXIT_ARM_TIMER guest exits when they are 
> pending,
> +unless masked by vcpu->run->request_interrupt_window (see 5.).
> +
>7. Capabilities that can be enabled on VMs
>--
>
> diff --git 

Re: [PATCH v4 2/2] KVM: arm/arm64: Route vtimer events to user space

[Marc Zyngier]

On 20/09/16 11:05, Alexander Graf wrote:
> On 09/20/2016 11:39 AM, Marc Zyngier wrote:
>> On 20/09/16 10:26, Alexander Graf wrote:
>>>
>>> On 20.09.16 11:21, Marc Zyngier wrote:
 On 19/09/16 18:39, Alexander Graf wrote:
>
> On 19.09.16 16:48, Marc Zyngier wrote:
>> On 19/09/16 12:14, Alexander Graf wrote:
>>> We have 2 modes for dealing with interrupts in the ARM world. We can 
>>> either
>>> handle them all using hardware acceleration through the vgic or we can 
>>> emulate
>>> a gic in user space and only drive CPU IRQ pins from there.
>>>
>>> Unfortunately, when driving IRQs from user space, we never tell user 
>>> space
>>> about timer events that may result in interrupt line state changes, so 
>>> we
>>> lose out on timer events if we run with user space gic emulation.
>>>
>>> This patch fixes that by routing vtimer expiration events to user space.
>>> With this patch I can successfully run edk2 and Linux with user space 
>>> gic
>>> emulation.
>>>
>>> Signed-off-by: Alexander Graf 
>>>
>>> ---
>>>
>>> v1 -> v2:
>>>
>>>- Add back curly brace that got lost
>>>
>>> v2 -> v3:
>>>
>>>- Split into patch set
>>>
>>> v3 -> v4:
>>>
>>>- Improve documentation
>>> ---
>>>   Documentation/virtual/kvm/api.txt |  30 -
>>>   arch/arm/include/asm/kvm_host.h   |   3 +
>>>   arch/arm/kvm/arm.c|  22 ---
>>>   arch/arm64/include/asm/kvm_host.h |   3 +
>>>   include/uapi/linux/kvm.h  |  14 +
>>>   virt/kvm/arm/arch_timer.c | 125 
>>> +++---
>>>   6 files changed, 155 insertions(+), 42 deletions(-)
>>>
>>> diff --git a/Documentation/virtual/kvm/api.txt 
>>> b/Documentation/virtual/kvm/api.txt
>>> index 23937e0..1c0bd86 100644
>>> --- a/Documentation/virtual/kvm/api.txt
>>> +++ b/Documentation/virtual/kvm/api.txt
>>> @@ -3202,9 +3202,14 @@ struct kvm_run {
>>> /* in */
>>> __u8 request_interrupt_window;
>>>   
>>> -Request that KVM_RUN return when it becomes possible to inject external
>>> +[x86] Request that KVM_RUN return when it becomes possible to inject 
>>> external
>>>   interrupts into the guest.  Useful in conjunction with KVM_INTERRUPT.
>>>   
>>> +[arm*] Bits set to 1 in here mask IRQ lines that would otherwise 
>>> potentially
>>> +trigger forever. These lines are available:
>>> +
>>> +KVM_IRQWINDOW_VTIMER  -  Masks hw virtual timer irq while in guest
>>> +
>>> __u8 padding1[7];
>>>   
>>> /* out */
>>> @@ -3519,6 +3524,18 @@ Hyper-V SynIC state change. Notification is used 
>>> to remap SynIC
>>>   event/message pages and to enable/disable SynIC messages/events 
>>> processing
>>>   in userspace.
>>>   
>>> +   /* KVM_EXIT_ARM_TIMER */
>>> +   struct {
>>> +   __u8 timesource;
>>> +   } arm_timer;
>>> +
>>> +Indicates that a timer triggered that user space needs to handle and
>>> +potentially mask with vcpu->run->request_interrupt_window to allow the
>>> +guest to proceed. This only happens for timers that got enabled through
>>> +KVM_CAP_ARM_TIMER. The following time sources are available:
>>> +
>>> +KVM_ARM_TIMER_VTIMER  - virtual cpu timer
>>> +
>>> /* Fix the size of the union. */
>>> char padding[256];
>>> };
>>> @@ -3739,6 +3756,17 @@ Once this is done the KVM_REG_MIPS_VEC_* and 
>>> KVM_REG_MIPS_MSA_* registers can be
>>>   accessed, and the Config5.MSAEn bit is accessible via the KVM API and 
>>> also from
>>>   the guest.
>>>   
>>> +6.11 KVM_CAP_ARM_TIMER
>>> +
>>> +Architectures: arm, arm64
>>> +Target: vcpu
>>> +Parameters: args[0] contains a bitmap of timers to select (see 5.)
>>> +
>>> +This capability allows to route per-core timers into user space. When 
>>> it's
>>> +enabled and no in-kernel interrupt controller is in use, the timers 
>>> selected
>>> +by args[0] trigger KVM_EXIT_ARM_TIMER guest exits when they are 
>>> pending,
>>> +unless masked by vcpu->run->request_interrupt_window (see 5.).
>>> +
>>>   7. Capabilities that can be enabled on VMs
>>>   --
>>>   
>>> diff --git a/arch/arm/include/asm/kvm_host.h 
>>> b/arch/arm/include/asm/kvm_host.h
>>> index de338d9..77d1f73 100644
>>> --- a/arch/arm/include/asm/kvm_host.h
>>> +++ b/arch/arm/include/asm/kvm_host.h
>>> @@ -180,6 +180,9 @@ struct kvm_vcpu_arch {
>>>   
>>> /* Detect first run of a vcpu */
>>> bool has_run_once;
>>> +
>>> +   /* User space 

Re: [PATCH v4 2/2] KVM: arm/arm64: Route vtimer events to user space

[Alexander Graf]

On 20.09.16 11:21, Marc Zyngier wrote:
> On 19/09/16 18:39, Alexander Graf wrote:
>>
>>
>> On 19.09.16 16:48, Marc Zyngier wrote:
>>> On 19/09/16 12:14, Alexander Graf wrote:
 We have 2 modes for dealing with interrupts in the ARM world. We can either
 handle them all using hardware acceleration through the vgic or we can 
 emulate
 a gic in user space and only drive CPU IRQ pins from there.

 Unfortunately, when driving IRQs from user space, we never tell user space
 about timer events that may result in interrupt line state changes, so we
 lose out on timer events if we run with user space gic emulation.

 This patch fixes that by routing vtimer expiration events to user space.
 With this patch I can successfully run edk2 and Linux with user space gic
 emulation.

 Signed-off-by: Alexander Graf 

 ---

 v1 -> v2:

   - Add back curly brace that got lost

 v2 -> v3:

   - Split into patch set

 v3 -> v4:

   - Improve documentation
 ---
  Documentation/virtual/kvm/api.txt |  30 -
  arch/arm/include/asm/kvm_host.h   |   3 +
  arch/arm/kvm/arm.c|  22 ---
  arch/arm64/include/asm/kvm_host.h |   3 +
  include/uapi/linux/kvm.h  |  14 +
  virt/kvm/arm/arch_timer.c | 125 
 +++---
  6 files changed, 155 insertions(+), 42 deletions(-)

 diff --git a/Documentation/virtual/kvm/api.txt 
 b/Documentation/virtual/kvm/api.txt
 index 23937e0..1c0bd86 100644
 --- a/Documentation/virtual/kvm/api.txt
 +++ b/Documentation/virtual/kvm/api.txt
 @@ -3202,9 +3202,14 @@ struct kvm_run {
/* in */
__u8 request_interrupt_window;
  
 -Request that KVM_RUN return when it becomes possible to inject external
 +[x86] Request that KVM_RUN return when it becomes possible to inject 
 external
  interrupts into the guest.  Useful in conjunction with KVM_INTERRUPT.
  
 +[arm*] Bits set to 1 in here mask IRQ lines that would otherwise 
 potentially
 +trigger forever. These lines are available:
 +
 +KVM_IRQWINDOW_VTIMER  -  Masks hw virtual timer irq while in guest
 +
__u8 padding1[7];
  
/* out */
 @@ -3519,6 +3524,18 @@ Hyper-V SynIC state change. Notification is used to 
 remap SynIC
  event/message pages and to enable/disable SynIC messages/events processing
  in userspace.
  
 +  /* KVM_EXIT_ARM_TIMER */
 +  struct {
 +  __u8 timesource;
 +  } arm_timer;
 +
 +Indicates that a timer triggered that user space needs to handle and
 +potentially mask with vcpu->run->request_interrupt_window to allow the
 +guest to proceed. This only happens for timers that got enabled through
 +KVM_CAP_ARM_TIMER. The following time sources are available:
 +
 +KVM_ARM_TIMER_VTIMER  - virtual cpu timer
 +
/* Fix the size of the union. */
char padding[256];
};
 @@ -3739,6 +3756,17 @@ Once this is done the KVM_REG_MIPS_VEC_* and 
 KVM_REG_MIPS_MSA_* registers can be
  accessed, and the Config5.MSAEn bit is accessible via the KVM API and 
 also from
  the guest.
  
 +6.11 KVM_CAP_ARM_TIMER
 +
 +Architectures: arm, arm64
 +Target: vcpu
 +Parameters: args[0] contains a bitmap of timers to select (see 5.)
 +
 +This capability allows to route per-core timers into user space. When it's
 +enabled and no in-kernel interrupt controller is in use, the timers 
 selected
 +by args[0] trigger KVM_EXIT_ARM_TIMER guest exits when they are pending,
 +unless masked by vcpu->run->request_interrupt_window (see 5.).
 +
  7. Capabilities that can be enabled on VMs
  --
  
 diff --git a/arch/arm/include/asm/kvm_host.h 
 b/arch/arm/include/asm/kvm_host.h
 index de338d9..77d1f73 100644
 --- a/arch/arm/include/asm/kvm_host.h
 +++ b/arch/arm/include/asm/kvm_host.h
 @@ -180,6 +180,9 @@ struct kvm_vcpu_arch {
  
/* Detect first run of a vcpu */
bool has_run_once;
 +
 +  /* User space wants timer notifications */
 +  bool user_space_arm_timers;
>>>
>>> Please move this to the timer structure.
>>
>> Sure.
>>
>>>
  };
  
  struct kvm_vm_stat {
 diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
 index c84b6ad..57bdb71 100644
 --- a/arch/arm/kvm/arm.c
 +++ b/arch/arm/kvm/arm.c
 @@ -187,6 +187,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long 
 ext)
case KVM_CAP_ARM_PSCI_0_2:
case KVM_CAP_READONLY_MEM:
case KVM_CAP_MP_STATE:
 +  case KVM_CAP_ARM_TIMER:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
 @@ 

Re: [PATCH v4 2/2] KVM: arm/arm64: Route vtimer events to user space

[Marc Zyngier]

On 19/09/16 18:39, Alexander Graf wrote:
> 
> 
> On 19.09.16 16:48, Marc Zyngier wrote:
>> On 19/09/16 12:14, Alexander Graf wrote:
>>> We have 2 modes for dealing with interrupts in the ARM world. We can either
>>> handle them all using hardware acceleration through the vgic or we can 
>>> emulate
>>> a gic in user space and only drive CPU IRQ pins from there.
>>>
>>> Unfortunately, when driving IRQs from user space, we never tell user space
>>> about timer events that may result in interrupt line state changes, so we
>>> lose out on timer events if we run with user space gic emulation.
>>>
>>> This patch fixes that by routing vtimer expiration events to user space.
>>> With this patch I can successfully run edk2 and Linux with user space gic
>>> emulation.
>>>
>>> Signed-off-by: Alexander Graf 
>>>
>>> ---
>>>
>>> v1 -> v2:
>>>
>>>   - Add back curly brace that got lost
>>>
>>> v2 -> v3:
>>>
>>>   - Split into patch set
>>>
>>> v3 -> v4:
>>>
>>>   - Improve documentation
>>> ---
>>>  Documentation/virtual/kvm/api.txt |  30 -
>>>  arch/arm/include/asm/kvm_host.h   |   3 +
>>>  arch/arm/kvm/arm.c|  22 ---
>>>  arch/arm64/include/asm/kvm_host.h |   3 +
>>>  include/uapi/linux/kvm.h  |  14 +
>>>  virt/kvm/arm/arch_timer.c | 125 
>>> +++---
>>>  6 files changed, 155 insertions(+), 42 deletions(-)
>>>
>>> diff --git a/Documentation/virtual/kvm/api.txt 
>>> b/Documentation/virtual/kvm/api.txt
>>> index 23937e0..1c0bd86 100644
>>> --- a/Documentation/virtual/kvm/api.txt
>>> +++ b/Documentation/virtual/kvm/api.txt
>>> @@ -3202,9 +3202,14 @@ struct kvm_run {
>>> /* in */
>>> __u8 request_interrupt_window;
>>>  
>>> -Request that KVM_RUN return when it becomes possible to inject external
>>> +[x86] Request that KVM_RUN return when it becomes possible to inject 
>>> external
>>>  interrupts into the guest.  Useful in conjunction with KVM_INTERRUPT.
>>>  
>>> +[arm*] Bits set to 1 in here mask IRQ lines that would otherwise 
>>> potentially
>>> +trigger forever. These lines are available:
>>> +
>>> +KVM_IRQWINDOW_VTIMER  -  Masks hw virtual timer irq while in guest
>>> +
>>> __u8 padding1[7];
>>>  
>>> /* out */
>>> @@ -3519,6 +3524,18 @@ Hyper-V SynIC state change. Notification is used to 
>>> remap SynIC
>>>  event/message pages and to enable/disable SynIC messages/events processing
>>>  in userspace.
>>>  
>>> +   /* KVM_EXIT_ARM_TIMER */
>>> +   struct {
>>> +   __u8 timesource;
>>> +   } arm_timer;
>>> +
>>> +Indicates that a timer triggered that user space needs to handle and
>>> +potentially mask with vcpu->run->request_interrupt_window to allow the
>>> +guest to proceed. This only happens for timers that got enabled through
>>> +KVM_CAP_ARM_TIMER. The following time sources are available:
>>> +
>>> +KVM_ARM_TIMER_VTIMER  - virtual cpu timer
>>> +
>>> /* Fix the size of the union. */
>>> char padding[256];
>>> };
>>> @@ -3739,6 +3756,17 @@ Once this is done the KVM_REG_MIPS_VEC_* and 
>>> KVM_REG_MIPS_MSA_* registers can be
>>>  accessed, and the Config5.MSAEn bit is accessible via the KVM API and also 
>>> from
>>>  the guest.
>>>  
>>> +6.11 KVM_CAP_ARM_TIMER
>>> +
>>> +Architectures: arm, arm64
>>> +Target: vcpu
>>> +Parameters: args[0] contains a bitmap of timers to select (see 5.)
>>> +
>>> +This capability allows to route per-core timers into user space. When it's
>>> +enabled and no in-kernel interrupt controller is in use, the timers 
>>> selected
>>> +by args[0] trigger KVM_EXIT_ARM_TIMER guest exits when they are pending,
>>> +unless masked by vcpu->run->request_interrupt_window (see 5.).
>>> +
>>>  7. Capabilities that can be enabled on VMs
>>>  --
>>>  
>>> diff --git a/arch/arm/include/asm/kvm_host.h 
>>> b/arch/arm/include/asm/kvm_host.h
>>> index de338d9..77d1f73 100644
>>> --- a/arch/arm/include/asm/kvm_host.h
>>> +++ b/arch/arm/include/asm/kvm_host.h
>>> @@ -180,6 +180,9 @@ struct kvm_vcpu_arch {
>>>  
>>> /* Detect first run of a vcpu */
>>> bool has_run_once;
>>> +
>>> +   /* User space wants timer notifications */
>>> +   bool user_space_arm_timers;
>>
>> Please move this to the timer structure.
> 
> Sure.
> 
>>
>>>  };
>>>  
>>>  struct kvm_vm_stat {
>>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>>> index c84b6ad..57bdb71 100644
>>> --- a/arch/arm/kvm/arm.c
>>> +++ b/arch/arm/kvm/arm.c
>>> @@ -187,6 +187,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long 
>>> ext)
>>> case KVM_CAP_ARM_PSCI_0_2:
>>> case KVM_CAP_READONLY_MEM:
>>> case KVM_CAP_MP_STATE:
>>> +   case KVM_CAP_ARM_TIMER:
>>> r = 1;
>>> break;
>>> case KVM_CAP_COALESCED_MMIO:
>>> @@ -474,13 +475,7 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu 
>>> *vcpu)
>>> return ret;
>>> }
>>>  
>>> -   /*
>>> -* 

Re: [PATCH v4 2/2] KVM: arm/arm64: Route vtimer events to user space

[Alexander Graf]

On 19.09.16 16:48, Marc Zyngier wrote:
> On 19/09/16 12:14, Alexander Graf wrote:
>> We have 2 modes for dealing with interrupts in the ARM world. We can either
>> handle them all using hardware acceleration through the vgic or we can 
>> emulate
>> a gic in user space and only drive CPU IRQ pins from there.
>>
>> Unfortunately, when driving IRQs from user space, we never tell user space
>> about timer events that may result in interrupt line state changes, so we
>> lose out on timer events if we run with user space gic emulation.
>>
>> This patch fixes that by routing vtimer expiration events to user space.
>> With this patch I can successfully run edk2 and Linux with user space gic
>> emulation.
>>
>> Signed-off-by: Alexander Graf 
>>
>> ---
>>
>> v1 -> v2:
>>
>>   - Add back curly brace that got lost
>>
>> v2 -> v3:
>>
>>   - Split into patch set
>>
>> v3 -> v4:
>>
>>   - Improve documentation
>> ---
>>  Documentation/virtual/kvm/api.txt |  30 -
>>  arch/arm/include/asm/kvm_host.h   |   3 +
>>  arch/arm/kvm/arm.c|  22 ---
>>  arch/arm64/include/asm/kvm_host.h |   3 +
>>  include/uapi/linux/kvm.h  |  14 +
>>  virt/kvm/arm/arch_timer.c | 125 
>> +++---
>>  6 files changed, 155 insertions(+), 42 deletions(-)
>>
>> diff --git a/Documentation/virtual/kvm/api.txt 
>> b/Documentation/virtual/kvm/api.txt
>> index 23937e0..1c0bd86 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>> @@ -3202,9 +3202,14 @@ struct kvm_run {
>>  /* in */
>>  __u8 request_interrupt_window;
>>  
>> -Request that KVM_RUN return when it becomes possible to inject external
>> +[x86] Request that KVM_RUN return when it becomes possible to inject 
>> external
>>  interrupts into the guest.  Useful in conjunction with KVM_INTERRUPT.
>>  
>> +[arm*] Bits set to 1 in here mask IRQ lines that would otherwise potentially
>> +trigger forever. These lines are available:
>> +
>> +KVM_IRQWINDOW_VTIMER  -  Masks hw virtual timer irq while in guest
>> +
>>  __u8 padding1[7];
>>  
>>  /* out */
>> @@ -3519,6 +3524,18 @@ Hyper-V SynIC state change. Notification is used to 
>> remap SynIC
>>  event/message pages and to enable/disable SynIC messages/events processing
>>  in userspace.
>>  
>> +/* KVM_EXIT_ARM_TIMER */
>> +struct {
>> +__u8 timesource;
>> +} arm_timer;
>> +
>> +Indicates that a timer triggered that user space needs to handle and
>> +potentially mask with vcpu->run->request_interrupt_window to allow the
>> +guest to proceed. This only happens for timers that got enabled through
>> +KVM_CAP_ARM_TIMER. The following time sources are available:
>> +
>> +KVM_ARM_TIMER_VTIMER  - virtual cpu timer
>> +
>>  /* Fix the size of the union. */
>>  char padding[256];
>>  };
>> @@ -3739,6 +3756,17 @@ Once this is done the KVM_REG_MIPS_VEC_* and 
>> KVM_REG_MIPS_MSA_* registers can be
>>  accessed, and the Config5.MSAEn bit is accessible via the KVM API and also 
>> from
>>  the guest.
>>  
>> +6.11 KVM_CAP_ARM_TIMER
>> +
>> +Architectures: arm, arm64
>> +Target: vcpu
>> +Parameters: args[0] contains a bitmap of timers to select (see 5.)
>> +
>> +This capability allows to route per-core timers into user space. When it's
>> +enabled and no in-kernel interrupt controller is in use, the timers selected
>> +by args[0] trigger KVM_EXIT_ARM_TIMER guest exits when they are pending,
>> +unless masked by vcpu->run->request_interrupt_window (see 5.).
>> +
>>  7. Capabilities that can be enabled on VMs
>>  --
>>  
>> diff --git a/arch/arm/include/asm/kvm_host.h 
>> b/arch/arm/include/asm/kvm_host.h
>> index de338d9..77d1f73 100644
>> --- a/arch/arm/include/asm/kvm_host.h
>> +++ b/arch/arm/include/asm/kvm_host.h
>> @@ -180,6 +180,9 @@ struct kvm_vcpu_arch {
>>  
>>  /* Detect first run of a vcpu */
>>  bool has_run_once;
>> +
>> +/* User space wants timer notifications */
>> +bool user_space_arm_timers;
> 
> Please move this to the timer structure.

Sure.

> 
>>  };
>>  
>>  struct kvm_vm_stat {
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index c84b6ad..57bdb71 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -187,6 +187,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long 
>> ext)
>>  case KVM_CAP_ARM_PSCI_0_2:
>>  case KVM_CAP_READONLY_MEM:
>>  case KVM_CAP_MP_STATE:
>> +case KVM_CAP_ARM_TIMER:
>>  r = 1;
>>  break;
>>  case KVM_CAP_COALESCED_MMIO:
>> @@ -474,13 +475,7 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu 
>> *vcpu)
>>  return ret;
>>  }
>>  
>> -/*
>> - * Enable the arch timers only if we have an in-kernel VGIC
>> - * and it has been properly initialized, since we cannot handle
>> - * interrupts from the virtual timer