Hi Eric,

On 2021-01-27 17:53, Auger Eric wrote:

Hi Marc,

On 1/25/21 1:26 PM, Marc Zyngier wrote:

quoted

Upgrading the PMU code from ARMv8.1 to ARMv8.4 turns out to be
pretty easy. All that is required is support for PMMIR_EL1, which
is read-only, and for which returning 0 is a valid option as long
as we don't advertise STALL_SLOT as an implemented event.

Let's just do that and adjust what we return to the guest.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/sysreg.h |  3 +++
 arch/arm64/kvm/pmu-emul.c       |  6 ++++++
 arch/arm64/kvm/sys_regs.c       | 11 +++++++----
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/sysreg.h 

b/arch/arm64/include/asm/sysreg.h
index 8b5e7e5c3cc8..2fb3f386588c 100644

--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h

@@ -846,7 +846,10 @@

 #define ID_DFR0_PERFMON_SHIFT		24

+#define ID_DFR0_PERFMON_8_0		0x3
 #define ID_DFR0_PERFMON_8_1		0x4
+#define ID_DFR0_PERFMON_8_4		0x5
+#define ID_DFR0_PERFMON_8_5		0x6

 #define ID_ISAR4_SWP_FRAC_SHIFT		28
 #define ID_ISAR4_PSR_M_SHIFT		24

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 398f6df1bbe4..72cd704a8368 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c

@@ -795,6 +795,12 @@ u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, 

bool pmceid1)
 		base = 0;
 	} else {
 		val = read_sysreg(pmceid1_el0);
+		/*
+		 * Don't advertise STALL_SLOT, as PMMIR_EL0 is handled
+		 * as RAZ
+		 */
+		if (vcpu->kvm->arch.pmuver >= ID_AA64DFR0_PMUVER_8_4)
+			val &= ~BIT_ULL(ARMV8_PMUV3_PERFCTR_STALL_SLOT - 32);

what about the STALL_SLOT_BACKEND and FRONTEND events then?

Aren't these a mandatory ARMv8.1 feature? I don't see a reason to
drop them.

quoted

 		base = 32;
 	}

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 8f79ec1fffa7..5da536ab738d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c

@@ -1051,16 +1051,16 @@ static u64 read_id_reg(const struct kvm_vcpu 

*vcpu,
 		/* Limit debug to ARMv8.0 */
 		val &= ~FEATURE(ID_AA64DFR0_DEBUGVER);
 		val |= FIELD_PREP(FEATURE(ID_AA64DFR0_DEBUGVER), 6);
-		/* Limit guests to PMUv3 for ARMv8.1 */
+		/* Limit guests to PMUv3 for ARMv8.4 */
 		val = cpuid_feature_cap_perfmon_field(val,
 						      ID_AA64DFR0_PMUVER_SHIFT,
-						      kvm_vcpu_has_pmu(vcpu) ? ID_AA64DFR0_PMUVER_8_1 : 0);
+						      kvm_vcpu_has_pmu(vcpu) ? ID_AA64DFR0_PMUVER_8_4 : 0);
 		break;
 	case SYS_ID_DFR0_EL1:
-		/* Limit guests to PMUv3 for ARMv8.1 */
+		/* Limit guests to PMUv3 for ARMv8.4 */
 		val = cpuid_feature_cap_perfmon_field(val,
 						      ID_DFR0_PERFMON_SHIFT,
-						      kvm_vcpu_has_pmu(vcpu) ? ID_DFR0_PERFMON_8_1 : 0);
+						      kvm_vcpu_has_pmu(vcpu) ? ID_DFR0_PERFMON_8_4 : 0);
 		break;
 	}

@@ -1496,6 +1496,7 @@ static const struct sys_reg_desc sys_reg_descs[] 

= {

 	{ SYS_DESC(SYS_PMINTENSET_EL1), access_pminten, reset_unknown, 
PMINTENSET_EL1 },
 	{ SYS_DESC(SYS_PMINTENCLR_EL1), access_pminten, reset_unknown, 
PMINTENSET_EL1 },

"KVM: arm64: Hide PMU registers from userspace when not available"
changed the above, doesn't it?

Yes, that's because the fix didn't make it in mainline before
5.11-rc5, and I based this on -rc4. I'll fix it at merge time.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...