Subject: [PATCH v2 2/5] KVM: ARM: on IO mem abort - route the call to KVM MMIO bus

From: [email-masked] (Christoffer Dall)
Date: Tue, 27 Jan 2015 22:38:53 +0100

On Sat, Jan 24, 2015 at 03:02:33AM +0200, Nikolay Nikolaev wrote:
> On Mon, Jan 12, 2015 at 7:09 PM, Eric Auger <[email-masked]> wrote:
> > Hi Nikolay,
> > On 12/07/2014 10:37 AM, 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..e42469f 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;
> >>  }
> >>
> >> +/**
> >> + * handle_kernel_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;
> > in case ret < 0 (-EOPNOTSUPP = -95) aren't we returning true too? return
> > (ret==0)?
> >
> >> +}
> >> +
> >>  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;
> >> +
> >>       kvm_prepare_mmio(run, &mmio);
> >>       return 0;
> > currently the io_mem_abort returned value is not used by mmu.c code. I
> > think this should be handed in kvm_handle_guest_abort. What do you think?
> 
> You're right that the returned value is not handled further after we
> exit io_mem_abort, it's just passed up the call stack.
> However I'm not sure how to handle it better. If you have ideas, please share.
> 
I'm confused: the return value from io_mem_abort is assigned to a
variable 'ret' in kvm_handle_guest_abort and that determines if we
should run the VM again or return to userspace (with some work for
userspace to do or with an error).

-Christoffer