Subject: [PATCH v2 03/15] arm/arm64: KVM: refactor vgic_handle_mmio() function

From: [email-masked] (Andre Przywara)
Date: Fri, 31 Oct 2014 13:42:16 +0000

Hi Christoffer,

On 15/10/14 17:25, Christoffer Dall wrote:
> On Thu, Aug 21, 2014 at 02:06:44PM +0100, Andre Przywara wrote:
>> Currently we only need to deal with one MMIO region for the GIC
>> emulation, but we soon need to extend this. Refactor the existing
>> code to allow easier addition of different ranges without code
>> duplication.
>>
>> Signed-off-by: Andre Przywara <[email-masked]>
>> ---
>>  virt/kvm/arm/vgic.c |   72 ++++++++++++++++++++++++++++++++++++---------------
>>  1 file changed, 51 insertions(+), 21 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>> index bba8692..3b6f78d 100644
>> --- a/virt/kvm/arm/vgic.c
>> +++ b/virt/kvm/arm/vgic.c
>> @@ -925,37 +925,28 @@ static bool vgic_validate_access(const struct vgic_dist *dist,
>>      return true;
>>  }
>>
>> -/**
>> - * vgic_handle_mmio - handle an in-kernel MMIO access
>> +/*
>> + * vgic_handle_mmio_range - 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
>> + * @ranges: pointer to the register defining structure
>> + * @mmio_base:      base address for this mapping
>>   *
>> - * returns true if the MMIO access has been performed in kernel space,
>> - * and false if it needs to be emulated in user space.
>> + * returns true if the MMIO access could be performed
>>   */
>> -bool vgic_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>> -                  struct kvm_exit_mmio *mmio)
>> +static bool vgic_handle_mmio_range(struct kvm_vcpu *vcpu, struct kvm_run *run,
>> +                        struct kvm_exit_mmio *mmio,
>> +                        const struct mmio_range *ranges,
>> +                        unsigned long mmio_base)
>
> now when we're chopping this up and about to add more logic based on
> our struct mmio_range, I think we should really consider getting rid of
> that comment abou the kvm_bus_io_*() API or actually use that API.

So I did some research in this area. The API is meant to separate
devices on a bus, so we would still need the structure to tell the
single registers apart. The users of kvm_io_bus do this all in one
switch/case, which would mean a step back in our case. Also we need more
members than just base and length.
So though I didn't try it, I guess it wouldn't be a win for us, I am not
even sure it would produce less code.
So I am more looking at removing the comment.

>
>>  {
>>      const struct mmio_range *range;
>>      struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
>> -    unsigned long base = dist->vgic_dist_base;
>>      bool updated_state;
>>      unsigned long offset;
>>
>> -    if (!irqchip_in_kernel(vcpu->kvm) ||
>> -        mmio->phys_addr < base ||
>> -        (mmio->phys_addr + mmio->len) > (base + KVM_VGIC_V2_DIST_SIZE))
>> -            return false;
>> -
>> -    /* We don't support ldrd / strd or ldm / stm to the emulated vgic */
>> -    if (mmio->len > 4) {
>> -            kvm_inject_dabt(vcpu, mmio->phys_addr);
>> -            return true;
>> -    }
>> -
>> -    offset = mmio->phys_addr - base;
>> -    range = find_matching_range(vgic_dist_ranges, mmio, offset);
>> +    offset = mmio->phys_addr - mmio_base;
>> +    range = find_matching_range(ranges, mmio, offset);
>>      if (unlikely(!range || !range->handle_mmio)) {
>>              pr_warn("Unhandled access %d %08llx %d\n",
>>                      mmio->is_write, mmio->phys_addr, mmio->len);
>> @@ -963,7 +954,7 @@ bool vgic_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>      }
>>
>>      spin_lock(&vcpu->kvm->arch.vgic.lock);
>> -    offset = mmio->phys_addr - range->base - base;
>> +    offset -= range->base;
>>      if (vgic_validate_access(dist, range, offset)) {
>>              updated_state = range->handle_mmio(vcpu, mmio, offset);
>>      } else {
>> @@ -981,6 +972,45 @@ bool vgic_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>      return true;
>>  }
>>
>> +#define IS_IN_RANGE(addr, alen, base, len) \
>> +    (((addr) >= (base)) && (((addr) + (alen)) < ((base) + (len))))
>
> that should be <= ((base) + (len)) right?

Indeed, thanks for spotting.
>
> that's a lot of parenthesis, how about creating a static inline instead?
>
> you could also rename alen to access_len

Will fix this.

Cheers,
Andre.

>
>> +
>> +static bool vgic_v2_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>> +                            struct kvm_exit_mmio *mmio)
>> +{
>> +    unsigned long base = vcpu->kvm->arch.vgic.vgic_dist_base;
>> +
>> +    if (!IS_IN_RANGE(mmio->phys_addr, mmio->len, base,
>> +                     KVM_VGIC_V2_DIST_SIZE))
>> +            return false;
>> +
>> +    /* GICv2 does not support accesses wider than 32 bits */
>> +    if (mmio->len > 4) {
>> +            kvm_inject_dabt(vcpu, mmio->phys_addr);
>> +            return true;
>> +    }
>> +
>> +    return vgic_handle_mmio_range(vcpu, run, mmio, vgic_dist_ranges, base);
>> +}
>> +
>> +/**
>> + * vgic_handle_mmio - handle an in-kernel MMIO access for the GIC emulation
>> + * @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.
>> + */
>> +bool vgic_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>> +                  struct kvm_exit_mmio *mmio)
>> +{
>> +    if (!irqchip_in_kernel(vcpu->kvm))
>> +            return false;
>> +
>> +    return vgic_v2_handle_mmio(vcpu, run, mmio);
>> +}
>> +
>>  static u8 *vgic_get_sgi_sources(struct vgic_dist *dist, int vcpu_id, int sgi)
>>  {
>>      return dist->irq_sgi_sources + vcpu_id * VGIC_NR_SGIS + sgi;
>> --
>> 1.7.9.5
>>
>
> Thanks,
> -Christoffer
>

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