Hi Marc,
On 1/4/21 5:27 PM, Marc Zyngier wrote:
> KVM_ARM_PMU only existed for the benefit of 32bit ARM hosts,
> and makes no sense now that we are 64bit only. Get rid of it.
>
> Signed-off-by: Marc Zyngier <m...@kernel.org>
> ---
> arch/arm64/kvm/Kconfig | 8 --------
> arch/arm64/kvm/Makefile | 2 +-
> include/kvm/arm_pmu.h | 2 +-
> 3 files changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 043756db8f6e..3964acf5451e 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -49,14 +49,6 @@ if KVM
>
> source "virt/kvm/Kconfig"
>
> -config KVM_ARM_PMU
> - bool "Virtual Performance Monitoring Unit (PMU) support"
> - depends on HW_PERF_EVENTS
> - default y
> - help
> - Adds support for a virtual Performance Monitoring Unit (PMU) in
> - virtual machines.
> -
> endif # KVM
>
> endif # VIRTUALIZATION
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 60fd181df624..13b017284bf9 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -24,4 +24,4 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o
> $(KVM)/eventfd.o \
> vgic/vgic-mmio-v3.o vgic/vgic-kvm-device.o \
> vgic/vgic-its.o vgic/vgic-debug.o
>
> -kvm-$(CONFIG_KVM_ARM_PMU) += pmu-emul.o
> +kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index fc85f50fa0e9..8dcb3e1477bc 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -13,7 +13,7 @@
> #define ARMV8_PMU_CYCLE_IDX (ARMV8_PMU_MAX_COUNTERS - 1)
> #define ARMV8_PMU_MAX_COUNTER_PAIRS ((ARMV8_PMU_MAX_COUNTERS + 1) >> 1)
>
> -#ifdef CONFIG_KVM_ARM_PMU
> +#ifdef CONFIG_HW_PERF_EVENTS
>
> struct kvm_pmc {
> u8 idx; /* index into the pmu->pmc array */
I grep'ed for KVM_ARM_PMU in the Linux sources, this patch takes care of all its
occurrences.
A few things popped into my mind when I saw the patch.
1. Replacing KVM_ARM_PMU with CONFIG_HW_PERF_EVENTS means it's not possible
anymore for the host to have perf support while KVM does not support emulating a
PMU. In this scenario, functions which would have been empty functions if
KVM_ARM_PMU was still around (I only found kvm_pmu_flush_hwstate() and
kvm_pmu_sync_hwstate() on the KVM_RUN path) will now be called and return early
after kvm_vcpu_has_pmu() returns 0. The overhead looks negligible to me, and I
don't think this configuration was common (especially since the default was y).
2. I did a grep for the files that include arm_pmu.h, and all the files were in
arch/arm64. I suppose arm_pmu.h exists in include/kvm instead of
arch/arm64/include/asm because it was shared with KVM/arm when it was still
around, right? Or is there another reason for that?
[1] https://www.spinics.net/lists/kvm-arm/msg44184.html
Thanks,
Alex
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