Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <5c227ef8-72d2-9254-f061-128974a6dc7d@gmail.com>
Date:   Thu, 28 Apr 2022 21:40:05 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.8.1
Subject: Re: [PATCH v4 6/7] perf/x86/amd/core: Add PerfMonV2 overflow handling
Content-Language: en-US
To:     Sandipan Das <sandipan.das@amd.com>
Cc:     peterz@infradead.org, bp@alien8.de, dave.hansen@linux.intel.com,
        acme@kernel.org, mark.rutland@arm.com,
        alexander.shishkin@linux.intel.com, namhyung@kernel.org,
        jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com,
        pbonzini@redhat.com, jmattson@google.com, eranian@google.com,
        puwen@hygon.cn, ananth.narayan@amd.com, ravi.bangoria@amd.com,
        santosh.shukla@amd.com,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-perf-users@vger.kernel.org, x86@kernel.org
References: <cover.1651058600.git.sandipan.das@amd.com>
 <6bb3a6de79afbdb1ebc1b804fb8c2002c00cbaee.1651058600.git.sandipan.das@amd.com>
From:   Like Xu <like.xu.linux@gmail.com>
Organization: Tencent
In-Reply-To: <6bb3a6de79afbdb1ebc1b804fb8c2002c00cbaee.1651058600.git.sandipan.das@amd.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 27/4/2022 7:31 pm, Sandipan Das wrote:
> +static inline void amd_pmu_ack_global_status(u64 status)
> +{
> +	/*
> +	 * PerfCntrGlobalStatus is read-only but an overflow acknowledgment

If wrmsrl PerfCntrGlobalStatus, remain silent or report #GP ?

> +	 * mechanism exists; writing 1 to a bit in PerfCntrGlobalStatusClr
> +	 * clears the same bit in PerfCntrGlobalStatus
> +	 */
> +
> +	/* Only allow modifications to PerfCntrGlobalStatus.PerfCntrOvfl */
> +	status &= amd_pmu_global_cntr_mask;
> +	wrmsrl(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR, status);

If rdmsrl PerfCntrGlobalStatusClr, does it return 0 or the value of 
PerfCntrGlobalStatus ?

> +}