Subject: [RFC PATCH 2/5] ARM: on IO mem abort - route the call to KVM MMIO bus

From: [email-masked] (Eric Auger)
Date: Mon, 12 Jan 2015 17:21:28 +0100

On 12/05/2014 01:06 PM, Nikolay Nikolaev wrote:
> On Sat, Nov 29, 2014 at 1:28 PM, Christoffer Dall
> <[email-masked]> wrote:
>> On Mon, Nov 24, 2014 at 11:26:51PM +0200, Nikolay Nikolaev wrote:
>>> On IO memory abort, try to handle the MMIO access thorugh the KVM
>>> registered read/write callbacks. This is done by invoking the relevant
>>> kvm_io_bus_* API.
>>>
>>> Signed-off-by: Nikolay Nikolaev <[email-masked]>
>>> ---
>>>  arch/arm/kvm/mmio.c |   33 +++++++++++++++++++++++++++++++++
>>>  1 file changed, 33 insertions(+)
>>>
>>> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
>>> index 4cb5a93..81230da 100644
>>> --- a/arch/arm/kvm/mmio.c
>>> +++ b/arch/arm/kvm/mmio.c
>>> @@ -162,6 +162,36 @@ static int decode_hsr(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>>       return 0;
>>>  }
>>>
>>> +/**
>>> + * kvm_handle_mmio - handle an in-kernel MMIO access
>>> + * @vcpu:    pointer to the vcpu performing the access
>>> + * @run:     pointer to the kvm_run structure
>>> + * @mmio:    pointer to the data describing the access
>>> + *
>>> + * returns true if the MMIO access has been performed in kernel space,
>>> + * and false if it needs to be emulated in user space.
>>> + */
>>> +static bool handle_kernel_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>> +             struct kvm_exit_mmio *mmio)
>>> +{
>>> +     int ret;
>>> +
>>> +     if (mmio->is_write) {
>>> +             ret = kvm_io_bus_write(vcpu, KVM_MMIO_BUS, mmio->phys_addr,
>>> +                             mmio->len, &mmio->data);
>>> +
>>> +     } else {
>>> +             ret = kvm_io_bus_read(vcpu, KVM_MMIO_BUS, mmio->phys_addr,
>>> +                             mmio->len, &mmio->data);
>>> +     }
>>> +     if (!ret) {
>>> +             kvm_prepare_mmio(run, mmio);
>>> +             kvm_handle_mmio_return(vcpu, run);
>>> +     }
>>> +
>>> +     return !ret;
>>> +}
>>> +
>>>  int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>>                phys_addr_t fault_ipa)
>>>  {
>>> @@ -200,6 +230,9 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>>       if (vgic_handle_mmio(vcpu, run, &mmio))
>>>               return 1;
>>>
>>> +     if (handle_kernel_mmio(vcpu, run, &mmio))
>>> +             return 1;
>>> +
>>
>> Is this stuff always synchronously handled so that the mmio is properly
>> populated upon handle_kernel_mmio on reads?
> 
> If I get it right the kvm_io_bus_ API is intended to work
> synchronously. Of course it probably depends
> on how the registered device handles the read/write call.
> Or maybe I misunderstand your question? Please clarify in that case.

in case of ioeventfd implementation it is not the case since the write
is deferred in the kernel thread which handles the eventfd.

Best Regards

Eric
> regards,
> Nikolay Nikolaev
>> -Christoffer