Hi Christoffer,
On 05/09/16 12:29, Christoffer Dall wrote:
> Hi Vladimir,
>
> I think commit title is too vague, can you be more specific?
>
KVM: arm: vgic-new: make extract_bytes to always work on 64-bit data
is it better?
> On Tue, Aug 16, 2016 at 11:46:54AM +0100, Vladimir Murzin wrote:
>> We have couple of 64-bit register defined in GICv3 architecture, so
>
> 'a couple', 'registers' (plural)
>
>> "unsigned long" kind of accessors wouldn't work for 32-bit. However,
>
> 'wouldn't work for 32-bit' is kind of generic as well. Perhaps you mean
> that unsigned long accesses to these registers will only access a single
> 32-bit work of that register.
>
>> these registers can't be access as 64-bit in a one go if we run 32-bit
>
> 'accessed', 's/in one go/with a single instruction/' ?
>
> 'a 32-bit host'
>
>> host simply because KVM doesn't support multiple load/store on MMIO
>
> by 'multiple load/store' you mean the 'load/store multiple' instructions
> specifically, right? Not a sequence of multiple loads and stores. I
> think you should be more specific here as well, for example, I think
> ldrd and strd are problematic as well.
>
>> space.
>>
>> It means that 32-bit guest access these registers in 32-bit chunks, so
>
> 'a 32-bit guest', 'accesses'
>
all suggestions you've made above are true. I'll rework commit message
to be more precise.
>> the only thing we need to do is to ensure that extract_bytes() always
>> takes 64-bit data.
>>
>> Since we are here fix couple of other width related issues by using
>> ULL variants over UL.
>>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
>> ---
>> virt/kvm/arm/vgic/vgic-mmio-v3.c | 6 +++---
>> virt/kvm/arm/vgic/vgic-mmio.h | 2 +-
>> 2 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
>> index ff668e0..cc20b60 100644
>> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
>> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
>> @@ -23,7 +23,7 @@
>> #include "vgic-mmio.h"
>>
>> /* extract @num bytes at @offset bytes offset in data */
>> -unsigned long extract_bytes(unsigned long data, unsigned int offset,
>> +unsigned long extract_bytes(u64 data, unsigned int offset,
>> unsigned int num)
>> {
>> return (data >> (offset * 8)) & GENMASK_ULL(num * 8 - 1, 0);
>> @@ -179,7 +179,7 @@ static unsigned long vgic_mmio_read_v3r_typer(struct kvm_vcpu *vcpu,
>> int target_vcpu_id = vcpu->vcpu_id;
>> u64 value;
>>
>> - value = (mpidr & GENMASK(23, 0)) << 32;
>> + value = (mpidr & GENMASK_ULL(23, 0)) << 32;
>
> why does this make a difference when mpidr is an unsigned long?
because we access a little bit further than unsigned long can accommodate
CC arch/arm/kvm/../../../virt/kvm/arm/vgic/vgic-mmio-v3.o
arch/arm/kvm/../../../virt/kvm/arm/vgic/vgic-mmio-v3.c: In function
'vgic_mmio_read_v3r_typer':
arch/arm/kvm/../../../virt/kvm/arm/vgic/vgic-mmio-v3.c:184:35: warning:
left shift count >= width of type [-Wshift-count-overflow]
value = (mpidr & GENMASK(23, 0)) << 32;
^
I can include this warning in commit message or maybe you want a
separate patch?
Vladimir
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