On 12/05/16 13:21, Christoffer Dall wrote:
> On Fri, May 06, 2016 at 11:45:49AM +0100, Andre Przywara wrote:
>> Since GICv3 supports much more than the 8 CPUs the GICv2 ITARGETSR
>> register can handle, the new IROUTER register covers the whole range
>> of possible target (V)CPUs by using the same MPIDR that the cores
>> report themselves.
>> In addition to translating this MPIDR into a vcpu pointer we store
>> the originally written value as well. The architecture allows to
>> write any values into the register, which must be read back as written.
>>
>> Since we don't support affinity level 3, we don't need to take care
>> about the upper word of this 64-bit register, which simplifies the
>> handling a bit.
>>
>> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
>> ---
>> Changelog RFC..v1:
>> - fold in and simplify vgic_v3_irq_change_affinity
>>
>> Changelog v1 .. v2:
>> - adapt to new MMIO framework
>>
>> virt/kvm/arm/vgic/vgic-mmio-v3.c | 65 +++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 64 insertions(+), 1 deletion(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
>> index 48fba9c..3bcc2c4 100644
>> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
>> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
>> @@ -86,6 +86,69 @@ static u32 compress_mpidr(unsigned long mpidr)
>> return ret;
>> }
>>
>> +static unsigned long decompress_mpidr(u32 value)
>> +{
>> + unsigned long mpidr;
>> +
>> + mpidr = ((value >> 0) & 0xFF) << MPIDR_LEVEL_SHIFT(0);
>> + mpidr |= ((value >> 8) & 0xFF) << MPIDR_LEVEL_SHIFT(1);
>> + mpidr |= ((value >> 16) & 0xFF) << MPIDR_LEVEL_SHIFT(2);
>> + mpidr |= (u64)((value >> 24) & 0xFF) << MPIDR_LEVEL_SHIFT(3);
>> +
>> + return mpidr;
>> +}
>> +
>> +static unsigned long vgic_mmio_read_irouter(struct kvm_vcpu *vcpu,
>> + gpa_t addr, unsigned int len)
>> +{
>> + int intid = (addr & 0x1fff) / 8;
>> + struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, NULL, intid);
>> + unsigned long mpidr;
>> +
>> + if (!irq)
>> + return 0;
>> +
>> + mpidr = decompress_mpidr(irq->mpidr);
>
> I'm unsure here; do we ned a READ_ONCE() in lieu taking the lock or are
> we guaranteed that this is a single memory access even with compiler
> inlining etc.?
I can't imagine the compiler being stupid enough to read this multiple
times, but better safe than sorry. +1 for READ_ONCE().
>
>> + return extract_bytes(mpidr, addr & 7, len);
>> +}
>> +
>> +static void vgic_mmio_write_irouter(struct kvm_vcpu *vcpu,
>> + gpa_t addr, unsigned int len,
>> + unsigned long val)
>> +{
>> + int intid = (addr & 0x1fff) / 8;
>> + struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, NULL, intid);
>> + unsigned long mask = 0xffffffff; /* upper word is WI */
>> + u64 mpidr;
>> +
>> + if (!irq)
>> + return;
>> +
>> + /*
>> + * There are only two supported options:
>> + * (1) aligned 64-bit access
>> + * (2) aligned 32-bit access
>> + *
>> + * TODO: make this check generic and move it to dispatch_...()
>> + */
>> + if (len != 4 && len != 8)
>> + return;
>> +
>> +
>> + /* The upper word is WI for us since we don't implement Aff3. */
>> + if (addr & 4)
>> + return;
>> +
>> + spin_lock(&irq->irq_lock);
>> +
>> + mpidr = decompress_mpidr(irq->mpidr);
>> + mpidr = (mpidr & ~mask) | (val & mask);
>> + irq->mpidr = compress_mpidr(mpidr);
>> + irq->target_vcpu = kvm_mpidr_to_vcpu(vcpu->kvm, mpidr);
>
> this is weird because it doesn't preserve read-as-written semantics but
> allows a guest to write something into the RES0 field and read that back
> in the Aff3 field...
I don't see how we get this RES0/Aff3 mixup, but I can see other issues:
>> + unsigned long mask = 0xffffffff; /* upper word is WI */
followed by:
>> + mpidr = (mpidr & ~mask) | (val & mask);
is not going to preserve the top bits on 32bit (assuming we could
perform a 64bit access on 32bit, but still). Also, the mask preserves
the IRM bit, which is wrong (we don't support 1-of-n distribution).
Why don't we just have
mpidr = val & GENMASK_ULL(23, 0);
and let's be done with it? I must be missing something about this whole
Aff3 thing...
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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