On 2021-01-27 17:41, Alexandru Elisei wrote:

Hi Marc,

Had another look at the patch, comments below.

On 1/25/21 12:26 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);

This is confusing the me. We have kvm->arch.pmuver set to the hardware
PMU version
(as set by __armv8pmu_probe_pmu()), but we ignore it when reporting the 
PMU
version to the guest. Why do we do that? We limit the event number in
kvm_pmu_event_mask() based on the hardware PMU version, so even if we 
advertise
Armv8.4 PMU, support for all those extra events added by Arm8.1 PMU is
missing (I hope I understood the code correctly).

That's a bit of mess-up. We obtain ID_AA64DFR0_EL1 from the sanitised
regs, but do most of our handling based on kvm->arch.pmuver. They really
should be the same, because that's what the sanitised registers give
you.

As for the events themselves, I don't get your drift. We do support
all the ARMv8.1 PMU events as long as the HW supports it, and we
don't lie to the guest about it either (cpuid_feature_cap_perfmon_field
does *cap* the field to some value, it doesn't allow it to increase
past what the HW supports).

I looked at commit c854188ea010 ("KVM: arm64: limit PMU version to 
PMUv3 for
ARMv8.1") which changed read_id_reg() to report PMUv3 for Armv8.1
unconditionally,
and there's no explanation why PMUv3 for Armv8.1 was chosen instead of
plain PMUv3 (PMUVer = 0b0100).

We picked ARMv8.1 because this is the first PMU revision that gives
you events in the 0x4000 range, all of which are available on
common ARMv8.2 HW.


Thanks,

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

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