Re: [PATCH 8/9] KVM: arm64: vgic-v3: Expose GICR_TYPER.Last for userspace

[Auger Eric]

Hi Alexandru,

On 1/12/21 6:02 PM, Alexandru Elisei wrote:
> Hi Eric,
> 
> On 12/12/20 6:50 PM, Eric Auger wrote:
>> Commit 23bde34771f1 ("KVM: arm64: vgic-v3: Drop the
>> reporting of GICR_TYPER.Last for userspace") temporarily fixed
>> a bug identified when attempting to access the GICR_TYPER
>> register before the redistributor region setting but dropped
>> the support of the LAST bit. This patch restores its
>> support (if the redistributor region was set) while keeping the
>> code safe.
> 
> I suppose the reason for emulating GICR_TYPER.Last is for architecture compliance,
> right? I think that should be in the commit message.
OK added this in the commit msg.
> 
>>
>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
>> ---
>>  arch/arm64/kvm/vgic/vgic-mmio-v3.c | 7 ++++++-
>>  include/kvm/arm_vgic.h             | 1 +
>>  2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> index 581f0f490000..2f9ef6058f6e 100644
>> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> @@ -277,6 +277,8 @@ static unsigned long vgic_uaccess_read_v3r_typer(struct kvm_vcpu *vcpu,
>>  						 gpa_t addr, unsigned int len)
>>  {
>>  	unsigned long mpidr = kvm_vcpu_get_mpidr_aff(vcpu);
>> +	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>> +	struct vgic_redist_region *rdreg = vgic_cpu->rdreg;
>>  	int target_vcpu_id = vcpu->vcpu_id;
>>  	u64 value;
>>  
>> @@ -286,7 +288,9 @@ static unsigned long vgic_uaccess_read_v3r_typer(struct kvm_vcpu *vcpu,
>>  	if (vgic_has_its(vcpu->kvm))
>>  		value |= GICR_TYPER_PLPIS;
>>  
>> -	/* reporting of the Last bit is not supported for userspace */
>> +	if (rdreg && (vgic_cpu->rdreg_index == (rdreg->free_index - 1)))
>> +		value |= GICR_TYPER_LAST;
>> +
>>  	return extract_bytes(value, addr & 7, len);
>>  }
>>  
>> @@ -714,6 +718,7 @@ int vgic_register_redist_iodev(struct kvm_vcpu *vcpu)
>>  		return -EINVAL;
>>  
>>  	vgic_cpu->rdreg = rdreg;
>> +	vgic_cpu->rdreg_index = rdreg->free_index;
> 
> What happens if the next redistributor region we register has the base address
> adjacent to this one?
> 
> I'm really not familiar with the code, but is it not possible to create two
> Redistributor regions (via
> KVM_DEV_ARM_VGIC_GRP_ADDR(KVM_VGIC_V3_ADDR_TYPE_REDIST)) where the second
> Redistributor region start address is immediately after the last Redistributor in
> the preceding region?
KVM_VGIC_V3_ADDR_TYPE_REDIST only allows to create a single rdist
region. Only KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION allows to register
several of them.

with KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION, it is possible to register
adjacent rdist regions. vgic_v3_rdist_free_slot() previously returned
the 1st rdist region where enough space remains for inserting the new
reg. We put the rdist at the free index there.

But maybe I misunderstood your question?

Thanks

Eric
> 
> Thanks,
> Alex
>>  
>>  	rd_base = rdreg->base + rdreg->free_index * KVM_VGIC_V3_REDIST_SIZE;
>>  
>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>> index a8d8fdcd3723..596c069263a7 100644
>> --- a/include/kvm/arm_vgic.h
>> +++ b/include/kvm/arm_vgic.h
>> @@ -322,6 +322,7 @@ struct vgic_cpu {
>>  	 */
>>  	struct vgic_io_device	rd_iodev;
>>  	struct vgic_redist_region *rdreg;
>> +	u32 rdreg_index;
>>  
>>  	/* Contains the attributes and gpa of the LPI pending tables. */
>>  	u64 pendbaser;
>