Re: [RFC 1/3] x86: KVM: stats: Add a stat to report status of APICv inhibition

Suthikulpanit, Suravee
2024-04-09T14:54:50Z

Hi

On 2/15/2024 11:01 PM, Alejandro Jimenez wrote:
> The inhibition status of APICv can currently be checked using the
> 'kvm_apicv_inhibit_changed' tracepoint, but this is not accessible if
> tracefs is not available (e.g. kernel lockdown, non-root user). Export
> inhibition status as a binary stat that can be monitored from userspace
> without elevated privileges.
>
> Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/x86.c | 10 +++++++++-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index ad5319a503f0..9b960a523715 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1524,6 +1524,7 @@ struct kvm_vm_stat {
> u64 nx_lpage_splits;
> u64 max_mmu_page_hash_collisions;
> u64 max_mmu_rmap_size;
> + u64 apicv_inhibited;
> };
>
> struct kvm_vcpu_stat {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b66c45e7f6f8..f7f598f066e7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -255,7 +255,8 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
> STATS_DESC_ICOUNTER(VM, pages_1g),
> STATS_DESC_ICOUNTER(VM, nx_lpage_splits),
> STATS_DESC_PCOUNTER(VM, max_mmu_rmap_size),
> - STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions)
> + STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions),
> + STATS_DESC_IBOOLEAN(VM, apicv_inhibited)

One use for this stats would be to help:
1. Determine if vm and/or vcpu is inhibited.
2. Determine the inhibit reason.

Therefore can we use STATS_DESC_ICOUNTER() instead of
STATS_DESC_IBOOLEAN(), and show the inhibit flag from

vm_reason = struct kvm->arch.apicv_inhibit_reasons
vcpu_reason = static_call(kvm_x86_vcpu_get_apicv_inhibit_reasons)(vcpu)

See kvm_vcpu_apicv_activated().

Thanks,
Suravee

> };
>
> const struct kvm_stats_header kvm_vm_stats_header = {
> @@ -10588,6 +10589,13 @@ void __kvm_set_or_clear_apicv_inhibit(struct kvm *kvm,
> */
> kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_UPDATE);
> kvm->arch.apicv_inhibit_reasons = new;
> +
> + /*
> + * Update inhibition statistic only when toggling APICv
> + * activation status.
> + */
> + kvm->stat.apicv_inhibited = !!new;
> +
> if (new) {
> unsigned long gfn = gpa_to_gfn(APIC_DEFAULT_PHYS_BASE);
> int idx = srcu_read_lock(&kvm->srcu);