Subject: [RFC PATCH 1/4] ARM: KVM: on unhandled IO mem abort, route the call to the KVM MMIO bus

From: [email-masked] (Paolo Bonzini)
Date: Sat, 29 Mar 2014 18:34:52 +0100

Il 28/03/2014 20:09, Christoffer Dall ha scritto:
> On Thu, Mar 13, 2014 at 04:57:26PM +0100, Antonios Motakis wrote:
>> On an unhandled IO memory abort, use the kvm_io_bus_* API in order to
>> handle the MMIO access through any registered read/write callbacks. This
>> is a dependency for eventfd support (ioeventfd and irqfd).
>>
>> However, accesses to the VGIC are still left implemented independently,
>> since the kvm_io_bus_* API doesn't pass the VCPU pointer doing the access.
>>
>> Signed-off-by: Antonios Motakis <[email-masked]>
>> Signed-off-by: Nikolay Nikolaev <[email-masked]>
>> ---
>>  arch/arm/kvm/mmio.c | 32 ++++++++++++++++++++++++++++++++
>>  virt/kvm/arm/vgic.c |  5 ++++-
>>  2 files changed, 36 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
>> index 4cb5a93..1d17831 100644
>> --- a/arch/arm/kvm/mmio.c
>> +++ b/arch/arm/kvm/mmio.c
>> @@ -162,6 +162,35 @@ 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, KVM_MMIO_BUS, mmio->phys_addr,
>> +				mmio->len, &mmio->data);
>> +
>> +	} else {
>> +		ret = kvm_io_bus_read(vcpu->kvm, 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 +229,9 @@ 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;
>> +
>
> this special-casing of the vgic is now really terrible.  Is there
> anything holding you back from doing the necessary restructure of the
> kvm_bus_io_*() API instead?  That would allow us to get rid of the ugly
> Fix it! in the vgic driver as well.

It's also quite terrible in x86, for the same reason (see 
vcpu_mmio_write in arch/x86/kvm/x86.c).

Though I suppose moving vgic_handle_mmio to handle_kernel_mmio would 
ameliorate the situation a bit.

Paolo

> -Christoffer
>
>>  	kvm_prepare_mmio(run, &mmio);
>>  	return 0;
>>  }
>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>> index 8ca405c..afdecc3 100644
>> --- a/virt/kvm/arm/vgic.c
>> +++ b/virt/kvm/arm/vgic.c
>> @@ -849,13 +849,16 @@ struct mmio_range *find_matching_range(const struct mmio_range *ranges,
>>  }
>>
>>  /**
>> - * vgic_handle_mmio - handle an in-kernel MMIO access
>> + * vgic_handle_mmio - handle an in-kernel vgic 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.
>> + *
>> + * This is handled outside of kvm_handle_mmio because the kvm_io_bus only
>> + * passes the VM pointer, while we need the VCPU performing the access.
>>   */
>>  bool vgic_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  		      struct kvm_exit_mmio *mmio)
>> --
>> 1.8.3.2
>>