On 6/29/21 3:47 PM, Marc Zyngier wrote:

On Tue, 29 Jun 2021 14:16:55 +0100,
Alexandre Chartre [off-list ref] wrote:

quoted

Hi Marc,

On 6/29/21 11:06 AM, Marc Zyngier wrote:

quoted

Hi Alexandre,

[...]

quoted

quoted

So the sysreg is the only thing we should consider, and I think we
should drop the useless masking. There is at least another instance of
this in the PMU code (kvm_pmu_overflow_status()), and apart from
kvm_pmu_vcpu_reset(), only the sysreg accessors should care about the
masking to sanitise accesses.

What do you think?

I think you are right. PMCNTENSET_EL0 is already masked with
kvm_pmu_valid_counter_mask() so there's effectively no need to mask
it again when we use it. I will send an additional patch (on top of
this one) to remove useless masking. Basically, changes would be:

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index bab4b735a0cf..e0dfd7ce4ba0 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c

@@ -373,7 +373,6 @@ static u64 kvm_pmu_overflow_status(struct kvm_vcpu *vcpu)
                 reg = __vcpu_sys_reg(vcpu, PMOVSSET_EL0);
                 reg &= __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
                 reg &= __vcpu_sys_reg(vcpu, PMINTENSET_EL1);
-               reg &= kvm_pmu_valid_counter_mask(vcpu);
         }
          return reg;

@@ -564,21 +563,22 @@ void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
   */
  void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
  {
-       unsigned long mask = kvm_pmu_valid_counter_mask(vcpu);
+       unsigned long mask;
         int i;
          if (val & ARMV8_PMU_PMCR_E) {
                 kvm_pmu_enable_counter_mask(vcpu,
-                      __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask);
+                      __vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
         } else {
                 kvm_pmu_disable_counter_mask(vcpu,
-                      __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask);
+                      __vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
         }
          if (val & ARMV8_PMU_PMCR_C)
                 kvm_pmu_set_counter_value(vcpu, ARMV8_PMU_CYCLE_IDX, 0);
          if (val & ARMV8_PMU_PMCR_P) {
+               mask = kvm_pmu_valid_counter_mask(vcpu);

Careful here, this clashes with a fix from Alexandru that is currently
in -next (PMCR_EL0.P shouldn't reset the cycle counter) and aimed at
5.14. And whilst you're at it, consider moving the 'mask' declaration
here too.

quoted

                 for_each_set_bit(i, &mask, 32)
                         kvm_pmu_set_counter_value(vcpu, i, 0);
         }

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1a7968ad078c..2e406905760e 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c

@@ -845,7 +845,7 @@ static bool access_pmcnten(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
                         kvm_pmu_disable_counter_mask(vcpu, val);
                 }
         } else {
-               p->regval = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask;
+               p->regval = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
         }
          return true;

If you are cleaning up the read-side of sysregs, access_pminten() and
access_pmovs() could have some of your attention too.

Ok, so for now, I will just resubmit the initial patch with the commit
comment fixes. Then, look at all the mask cleanup on top of Alexandru
changes and prepare another patch.

alex.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel