Re: [PATCH v2] KVM: arm64: pmu: Resync EL0 state on counter rotation

From: Marc Zyngier <maz@kernel.org>
To: Alexander Stein <alexander.stein@ew.tq-group.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Huang Shijie <shijie@os.amperecomputing.com>,
	Leo Yan <leo.yan@linaro.org>, Mark Rutland <mark.rutland@arm.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH v2] KVM: arm64: pmu: Resync EL0 state on counter rotation
Date: Wed, 23 Aug 2023 10:21:45 +0100	[thread overview]
Message-ID: <86h6oqf712.wl-maz@kernel.org> (raw)
In-Reply-To: <14141350.uLZWGnKmhe@steina-w>

On Wed, 23 Aug 2023 08:15:38 +0100,
Alexander Stein <alexander.stein@ew.tq-group.com> wrote:
> 
> Hi,
> 
> > diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
> > index 08b3a1bf0ef6..6a3d8176f54a 100644
> > --- a/drivers/perf/arm_pmuv3.c
> > +++ b/drivers/perf/arm_pmuv3.c
> > @@ -772,6 +772,8 @@ static void armv8pmu_start(struct arm_pmu *cpu_pmu)
> > 
> >  	/* Enable all counters */
> >  	armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
> > +
> > +	kvm_vcpu_pmu_resync_el0();
> 
> This breaks if CONFIG_HW_PERF_EVENTS is enabled but CONFIG_KVM is not. As in 
> this case arch/arm64/kvm/pmu.c is never compiled, but the dummy inline in 
> include/kvm/arm_pmu.h for kvm_vcpu_pmu_resync_el0() only depends on 
> CONFIG_HW_PERF_EVENTS.
> This results in this error:
> 
> aarch64-v8a-linux-gnu-ld: Unexpected GOT/PLT entries detected!
> aarch64-v8a-linux-gnu-ld: Unexpected run-time procedure linkages detected!
> aarch64-v8a-linux-gnu-ld: drivers/perf/arm_pmuv3.o: in function 
> `armv8pmu_start':
> drivers/perf/arm_pmuv3.c:753: undefined reference to `kvm_vcpu_pmu_resync_el0'

Huh, that's unexpected. Let's fix it with an adequately sized hammer.
Does the patch below work for you?

Thanks,

	M.

From 2446f15d355ab7e766291eccf5b670a2060b4c3a Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@kernel.org>
Date: Wed, 23 Aug 2023 10:14:48 +0100
Subject: [PATCH] KVM: arm64: pmu: Guard PMU emulation definitions with
 CONFIG_KVM

Most of the internal definitions for PMU emulation are guarded with
CONFIG_HW_PERF_EVENTS. However, this isn't enough, and leads to
these definitions leaking if CONFIG_KVM isn't enabled.

This leads to some compilation breakage in this exact configuration.
Fix it by falling back to the dummy stubs if either perf or KVM
isn't selected.

Reported-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 include/kvm/arm_pmu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 3a8a70a60794..31029f4f7be8 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -12,7 +12,7 @@
 
 #define ARMV8_PMU_CYCLE_IDX		(ARMV8_PMU_MAX_COUNTERS - 1)
 
-#ifdef CONFIG_HW_PERF_EVENTS
+#if IS_ENABLED(CONFIG_HW_PERF_EVENTS) && IS_ENABLED(CONFIG_KVM)
 
 struct kvm_pmc {
 	u8 idx;	/* index into the pmu->pmc array */
-- 
2.34.1


-- 
Without deviation from the norm, progress is not possible.
