Subject: [PATCH v3 06/10] arm: simplify MMIO dispatching

From: [email-masked] (Marc Zyngier)
Date: Wed, 17 Jun 2015 15:06:34 +0100

On 17/06/15 14:49, Andre Przywara wrote:
> Hi Marc,
> 
> On 06/17/2015 01:48 PM, Marc Zyngier wrote:
>> On 17/06/15 12:21, Andre Przywara wrote:
>>> Currently we separate any incoming MMIO request into one of the ARM
>>> memory map regions and take care to spare the GIC.
>>> It turns out that this is unnecessary, as we only have one special
>>> region (the IO port area in the first 64 KByte). The MMIO rbtree
>>> takes care about unhandled MMIO ranges, so we can simply drop all the
>>> special range checking (except that for the IO range) in
>>> kvm_cpu__emulate_mmio().
>>> As the GIC is handled in the kernel, a GIC MMIO access should never
>>> reach userland (and we don't know what to do with it anyway).
>>> This lets us delete some more code and simplifies future extensions
>>> (like expanding the GIC regions).
>>> To be in line with the other architectures, move the now simpler
>>> code into a header file.
>>>
>>> Signed-off-by: Andre Przywara <[email-masked]>
>>> ---
>>>  arm/include/arm-common/kvm-arch.h     | 12 ------------
>>>  arm/include/arm-common/kvm-cpu-arch.h | 14 ++++++++++++--
>>>  arm/kvm-cpu.c                         | 16 ----------------
>>>  3 files changed, 12 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/arm/include/arm-common/kvm-arch.h b/arm/include/arm-common/kvm-arch.h
>>> index 082131d..90d6733 100644
>>> --- a/arm/include/arm-common/kvm-arch.h
>>> +++ b/arm/include/arm-common/kvm-arch.h
>>> @@ -45,18 +45,6 @@ static inline bool arm_addr_in_ioport_region(u64 phys_addr)
>>>  	return phys_addr >= KVM_IOPORT_AREA && phys_addr < limit;
>>>  }
>>>  
>>> -static inline bool arm_addr_in_virtio_mmio_region(u64 phys_addr)
>>> -{
>>> -	u64 limit = KVM_VIRTIO_MMIO_AREA + ARM_VIRTIO_MMIO_SIZE;
>>> -	return phys_addr >= KVM_VIRTIO_MMIO_AREA && phys_addr < limit;
>>> -}
>>> -
>>> -static inline bool arm_addr_in_pci_region(u64 phys_addr)
>>> -{
>>> -	u64 limit = KVM_PCI_CFG_AREA + ARM_PCI_CFG_SIZE + ARM_PCI_MMIO_SIZE;
>>> -	return phys_addr >= KVM_PCI_CFG_AREA && phys_addr < limit;
>>> -}
>>> -
>>>  struct kvm_arch {
>>>  	/*
>>>  	 * We may have to align the guest memory for virtio, so keep the
>>> diff --git a/arm/include/arm-common/kvm-cpu-arch.h b/arm/include/arm-common/kvm-cpu-arch.h
>>> index 36c7872..329979a 100644
>>> --- a/arm/include/arm-common/kvm-cpu-arch.h
>>> +++ b/arm/include/arm-common/kvm-cpu-arch.h
>>> @@ -44,8 +44,18 @@ static inline bool kvm_cpu__emulate_io(struct kvm_cpu *vcpu, u16 port, void *dat
>>>  	return false;
>>>  }
>>>  
>>> -bool kvm_cpu__emulate_mmio(struct kvm_cpu *vcpu, u64 phys_addr, u8 *data,
>>> -			   u32 len, u8 is_write);
>>> +static inline bool kvm_cpu__emulate_mmio(struct kvm_cpu *vcpu, u64 phys_addr,
>>> +					 u8 *data, u32 len, u8 is_write)
>>> +{
>>> +	if (arm_addr_in_ioport_region(phys_addr)) {
>>> +		int direction = is_write ? KVM_EXIT_IO_OUT : KVM_EXIT_IO_IN;
>>> +		u16 port = (phys_addr - KVM_IOPORT_AREA) & USHRT_MAX;
>>> +
>>> +		return kvm__emulate_io(vcpu, port, data, direction, len, 1);
>>> +	}
>>> +
>>> +	return kvm__emulate_mmio(vcpu, phys_addr, data, len, is_write);
>>> +}
>>>  
>>>  unsigned long kvm_cpu__get_vcpu_mpidr(struct kvm_cpu *vcpu);
>>>  
>>> diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
>>> index ab08815..7780251 100644
>>> --- a/arm/kvm-cpu.c
>>> +++ b/arm/kvm-cpu.c
>>> @@ -139,22 +139,6 @@ bool kvm_cpu__handle_exit(struct kvm_cpu *vcpu)
>>>  	return false;
>>>  }
>>>  
>>> -bool kvm_cpu__emulate_mmio(struct kvm_cpu *vcpu, u64 phys_addr, u8 *data,
>>> -			   u32 len, u8 is_write)
>>> -{
>>> -	if (arm_addr_in_virtio_mmio_region(phys_addr)) {
>>> -		return kvm__emulate_mmio(vcpu, phys_addr, data, len, is_write);
>>> -	} else if (arm_addr_in_ioport_region(phys_addr)) {
>>> -		int direction = is_write ? KVM_EXIT_IO_OUT : KVM_EXIT_IO_IN;
>>> -		u16 port = (phys_addr - KVM_IOPORT_AREA) & USHRT_MAX;
>>> -		return kvm__emulate_io(vcpu, port, data, direction, len, 1);
>>> -	} else if (arm_addr_in_pci_region(phys_addr)) {
>>> -		return kvm__emulate_mmio(vcpu, phys_addr, data, len, is_write);
>>> -	}
>>
>> Can you explain why this arm_addr_in_pci_region(phys_addr) check has
>> disappeared in your updated version on this function? It may be a non
>> issue, but I'd very much like to understand.
> 
> If you look above the calls to kvm__emulate_mmio() are exactly the same
> for the PCI and the virtio_mmio region, also as the areas are
> non-overlapping the if branches can be reordered.
> arm_addr_in_virtio_mmio_region() is true between 64k and (1GB - GIC),
> while arm_addr_in_pci_region() gives true between 1GB and 2GB.
> 
> So this translates into: do kvm__emulate_io() for anything below 64K and
> kvm__emulate_mmio() for everything else except for the GIC area,
> admittedly in a quite convoluted way.
> 
> So my patch just removes the check for the GIC region and rewrites it to
> match that description in the last sentence, with the rationale given in
> the commit message.
> Does that make sense?
> If you desperately want some extra barfing for misguided GIC requests,
> I'd rather introduce that to the "no match" code path in
> kvm__emulate_mmio or register some dummy MMIO regions for the GIC with
> panic() handlers.

No, that's fine.

I just wondered what was the rational behind having the
arm_addr_in_pci_region() call there. It might have guarded something,
but if you're absolutely positive that this doesn't cause a regression,
that's OK with me.

Reviewed-by: Marc Zyngier <[email-masked]>

	M.
-- 
Jazz is not dead. It just smells funny...