Re: [PATCH RFC V3 08/29] arm/virt: Init PMU at host for all possible vcpus

[Nicholas Piggin]

On Fri Jun 14, 2024 at 9:36 AM AEST, Salil Mehta wrote:
> PMU for all possible vCPUs must be initialized at the VM initialization time.
> Refactor existing code to accomodate possible vCPUs. This also assumes that 
> all
> processor being used are identical.
>
> Past discussion for reference:
> Link: https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00131.html

I guess it's something for the ARM people, but there's a lot of
information in there, could it be useful to summarise important
parts here, e.g., from Andrew:

 KVM requires all VCPUs to have a PMU if one does. If the ARM ARM
 says it's possible to have PMUs for only some CPUs, then, for TCG,
 the restriction could be relaxed.

(I assume he meant ARM arch)

>
> Co-developed-by: Salil Mehta <salil.mehta@huawei.com>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
>  hw/arm/virt.c         | 12 ++++++++----
>  include/hw/arm/virt.h |  1 +
>  2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index ac53bfadca..57ec429022 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2045,12 +2045,14 @@ static void finalize_gic_version(VirtMachineState 
> *vms)
>   */
>  static void virt_cpu_post_init(VirtMachineState *vms, MemoryRegion *sysmem)
>  {
> +    CPUArchIdList *possible_cpus = vms->parent.possible_cpus;
>      int max_cpus = MACHINE(vms)->smp.max_cpus;
> -    bool aarch64, pmu, steal_time;
> +    bool aarch64, steal_time;
>      CPUState *cpu;
> +    int n;
>  
>      aarch64 = object_property_get_bool(OBJECT(first_cpu), "aarch64", NULL);
> -    pmu = object_property_get_bool(OBJECT(first_cpu), "pmu", NULL);
> +    vms->pmu = object_property_get_bool(OBJECT(first_cpu), "pmu", NULL);
>      steal_time = object_property_get_bool(OBJECT(first_cpu),
>                                            "kvm-steal-time", NULL);
>  
> @@ -2077,8 +2079,10 @@ static void virt_cpu_post_init(VirtMachineState *vms, 
> MemoryRegion *sysmem)
>              memory_region_add_subregion(sysmem, pvtime_reg_base, pvtime);
>          }
>  
> -        CPU_FOREACH(cpu) {
> -            if (pmu) {
> +        for (n = 0; n < possible_cpus->len; n++) {
> +            cpu = qemu_get_possible_cpu(n);
> +

Maybe a CPU_FOREACH_POSSIBLE()?

Thanks,
Nick

> +            if (vms->pmu) {
>                  assert(arm_feature(&ARM_CPU(cpu)->env, ARM_FEATURE_PMU));
>                  if (kvm_irqchip_in_kernel()) {
>                      kvm_arm_pmu_set_irq(ARM_CPU(cpu), VIRTUAL_PMU_IRQ);
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 36ac5ff4a2..d8dcc89a0d 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -155,6 +155,7 @@ struct VirtMachineState {
>      bool ras;
>      bool mte;
>      bool dtb_randomness;
> +    bool pmu;
>      OnOffAuto acpi;
>      VirtGICType gic_version;
>      VirtIOMMUType iommu;