On 4/29/2024 9:27 PM, Alejandro Jimenez wrote:
> Add a stat to query when PIT is in reinject mode, which can have a large
> performance impact due to disabling SVM AVIC.
> When using in-kernel irqchip, QEMU and KVM default to creating a PIT in
> reinject mode, since this is necessary for old guest operating systems that
> use the PIT for timing. Unfortunately, reinject mode relies on EOI
> interception and so SVM AVIC must be inhibited when the PIT is set up using
> this mode.
>
> Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@xxxxxxxxxx>
Reviewed-by: Vasant Hegde <vasant.hegde@xxxxxxx>
-Vasant
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/i8254.c | 2 ++
> arch/x86/kvm/x86.c | 3 ++-
> 3 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index f3b40cfebec4..e7e3213cefae 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1535,6 +1535,7 @@ struct kvm_vm_stat {
> u64 max_mmu_page_hash_collisions;
> u64 max_mmu_rmap_size;
> u64 synic_auto_eoi_used;
> + u64 pit_reinject_mode;
> };
>
> struct kvm_vcpu_stat {
> diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> index cd57a517d04a..44e593e909a1 100644
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -316,6 +316,8 @@ void kvm_pit_set_reinject(struct kvm_pit *pit, bool reinject)
> kvm_unregister_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
> }
>
> + kvm->stat.pit_reinject_mode = reinject;
> +
> atomic_set(&ps->reinject, reinject);
> }
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 27e339133068..03cb933920cb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -257,7 +257,8 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
> 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_IBOOLEAN(VM, synic_auto_eoi_used)
> + STATS_DESC_IBOOLEAN(VM, synic_auto_eoi_used),
> + STATS_DESC_IBOOLEAN(VM, pit_reinject_mode)
> };
>
> const struct kvm_stats_header kvm_vm_stats_header = {
