linux-kernel - Re: [PATCH v3 1/7] KVM: x86/pmu: Avoid setting BIT_ULL(-1) to pmu->host_cross_mapped

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Date:   Thu, 22 Sep 2022 22:30:39 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/7] KVM: x86/pmu: Avoid setting BIT_ULL(-1) to
 pmu->host_cross_mapped_mask

On Wed, Aug 31, 2022, Like Xu wrote:
> +		hw_idx = pmc->perf_event->hw.idx;
> +		/* make it a little less dependent on perf's exact behavior */

Reworded this to explain how a negative value can be encountered.

> +		if (hw_idx != pmc->idx && hw_idx > -1)
> +			pmu->host_cross_mapped_mask |= BIT_ULL(hw_idx);
>  	}
>  }