Re: [PATCH v3 8/9] perf/x86/amd: Remove exclude_guest check from perf_ibs_init()

[Jim Mattson <jmattson@google.com>]

On Tue, Mar 10, 2026 at 06:00:20AM +0000, Manali Shukla wrote:
> Currently IBS driver doesn't allow the creation of IBS event with
> exclude_guest set. As a result, amd_ibs_init() returns -EINVAL if
> IBS event is created with exclude_guest set.

s/amd_ibs_init()/perf_ibs_init()/

> With the introduction of mediated PMU support, software-based handling
> of exclude_guest is permitted for PMUs that have the
> PERF_PMU_CAP_MEDIATED_VPMU capability.

This software-based handling applies only while a vCPU with a mediated
PMU is loaded (perf_load_guest_context() through perf_put_guest_context()).
The core PMU also sets AMD64_EVENTSEL_HOSTONLY for exclude_guest events,
so the hardware excludes guest execution in all other cases. IBS has no
equivalent, and nothing in the IBS driver or in KVM stops an IBS event
while a guest without a mediated PMU runs (for example, when
kvm_amd.enable_mediated_pmu=0, or when the VM is created with
KVM_PMU_CAP_DISABLE). After this patch, perf_ibs_init() accepts
exclude_guest=1 in those cases, but the event does not exclude the guest.
This seems like a problem.

> Since ibs_op and ibs_fetch pmus has PERF_PMU_CAP_MEDIATED_VPMU
> capability set, update perf_ibs_init() to remove exclude_guest check.

s/pmus has/PMUs have/

As I said on patch 7/9, please squash this patch with patch 7/9.

> Signed-off-by: Manali Shukla <manali.shukla@amd.com>
> ---
>  arch/x86/events/amd/ibs.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> index e075c5ed136c..47f4dc0b6341 100644
> --- a/arch/x86/events/amd/ibs.c
> +++ b/arch/x86/events/amd/ibs.c
> @@ -327,8 +327,7 @@ static int perf_ibs_init(struct perf_event *event)
>  		return -EOPNOTSUPP;
>
>  	/* handle exclude_{user,kernel} in the IRQ handler */
> -	if (event->attr.exclude_host || event->attr.exclude_guest ||
> -	    event->attr.exclude_idle)
> +	if (event->attr.exclude_host || event->attr.exclude_idle)
>  		return -EINVAL;
>
>  	ret = validate_group(event);