Re: [PATCH v2 13/25] KVM: arm64: vgic-v3: Add ICV_BPR0_EL1 handler

Christoffer Dall
2017-06-06T15:46:09Z

On Tue, Jun 06, 2017 at 04:15:05PM +0100, Marc Zyngier wrote:
> On 06/06/17 13:11, Christoffer Dall wrote:
> > On Thu, Jun 01, 2017 at 11:21:05AM +0100, Marc Zyngier wrote:
> >> Add a handler for reading/writing the guest's view of the ICC_BPR0_EL1
> >> register, which is located in the ICH_VMCR_EL2.BPR0 field.
> >>
> >> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> >> ---
> >> arch/arm64/include/asm/sysreg.h | 1 +
> >> virt/kvm/arm/hyp/vgic-v3-sr.c | 36 ++++++++++++++++++++++++++++++++++++
> >> 2 files changed, 37 insertions(+)
> >>
> >> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> >> index bd000686194a..d20be0b28ca4 100644
> >> --- a/arch/arm64/include/asm/sysreg.h
> >> +++ b/arch/arm64/include/asm/sysreg.h
> >> @@ -180,6 +180,7 @@
> >>
> >> #define SYS_VBAR_EL1 sys_reg(3, 0, 12, 0, 0)
> >>
> >> +#define SYS_ICC_BPR0_EL1 sys_reg(3, 0, 12, 8, 3)
> >> #define SYS_ICC_AP1Rn_EL1(n) sys_reg(3, 0, 12, 9, n)
> >> #define SYS_ICC_DIR_EL1 sys_reg(3, 0, 12, 11, 1)
> >> #define SYS_ICC_SGI1R_EL1 sys_reg(3, 0, 12, 11, 5)
> >> diff --git a/virt/kvm/arm/hyp/vgic-v3-sr.c b/virt/kvm/arm/hyp/vgic-v3-sr.c
> >> index 42ac9ee7650a..54a8e828c85b 100644
> >> --- a/virt/kvm/arm/hyp/vgic-v3-sr.c
> >> +++ b/virt/kvm/arm/hyp/vgic-v3-sr.c
> >> @@ -688,11 +688,41 @@ static void __hyp_text __vgic_v3_write_igrpen1(struct kvm_vcpu *vcpu, u32 vmcr,
> >> __vgic_v3_write_vmcr(vmcr);
> >> }
> >>
> >> +static void __hyp_text __vgic_v3_read_bpr0(struct kvm_vcpu *vcpu, u32 vmcr, int rt)
> >> +{
> >> + vcpu_set_reg(vcpu, rt, __vgic_v3_get_bpr0(vmcr));
> >> +}
> >> +
> >> static void __hyp_text __vgic_v3_read_bpr1(struct kvm_vcpu *vcpu, u32 vmcr, int rt)
> >> {
> >> vcpu_set_reg(vcpu, rt, __vgic_v3_get_bpr1(vmcr));
> >> }
> >>
> >> +static void __hyp_text __vgic_v3_write_bpr0(struct kvm_vcpu *vcpu, u32 vmcr, int rt)
> >> +{
> >> + u64 val = vcpu_get_reg(vcpu, rt);
> >> + u8 bpr_min = 7 - vtr_to_nr_pre_bits(read_gicreg(ICH_VTR_EL2));
> >> +
> >> + /* Enforce BPR limiting */
> >> + if (val < bpr_min)
> >> + val = bpr_min;
> >> +
> >> + val <<= ICH_VMCR_BPR0_SHIFT;
> >> + val &= ICH_VMCR_BPR0_MASK;
> >> + vmcr &= ~ICH_VMCR_BPR0_MASK;
> >> + vmcr |= val;
> >> +
> >> + if (vmcr & ICH_VMCR_CBPR_MASK) {
> >> + val = __vgic_v3_get_bpr1(vmcr);
> >> + val <<= ICH_VMCR_BPR1_SHIFT;
> >> + val &= ICH_VMCR_BPR1_MASK;
> >> + vmcr &= ~ICH_VMCR_BPR1_MASK;
> >> + vmcr |= val;
> >> + }
> >
> > I don't understand why this block is needed?
>
> If you have CBPR already set, and then update BPR0, you need to make
> sure that BPR1 gets updated as well. You could hope that the HW would do
> it for you, but since we're erratum workaround land...
>

I just didn't read the spec that way, I gathered that the hardware would
maintain read-as-written for for bpr1 but use bpr0 to set the binary
point when cbpr is set, and just ignore writes to bpr1 for as long as
cbpr is set.

In any case, probably doesn't matter, but I was just curious if the spec
dictateted this behavior and if we should reference that part of the
spec in a comment then.

Thanks,
-Christoffer