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AJvYcCWYL1BXY6+K9LF96x6WoyRBvpwJ6mrbxBXayXfUbjb4/FpL/3ImiKecZuKu5kCLkqNHSfkzq+fpddmvK9eBlITKpX8mfTx3cPjFNdMr X-Gm-Message-State: AOJu0YwyaqDKcHdvrybcpDIUm5b23D+up5AdaMhHO9v99eVSbk9wdaHp ZmWg1q2lQ5f6S27XAqKNiKZEO2nqgfZBuiEwNmbq5CQF+s/XDOAYfwHZvtiH9eXcArM9p9z10Je YZg== X-Google-Smtp-Source: AGHT+IEar8TRcdXvMuTPUVFnkSx1JlvfraxiBybj4p1JG6Jg8CcJxmn1OlXaUfN1eRDVQrA+4z/SonB6OCg= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a81:91d4:0:b0:615:32e1:d82c with SMTP id i203-20020a8191d4000000b0061532e1d82cmr67605ywg.6.1712861812259; Thu, 11 Apr 2024 11:56:52 -0700 (PDT) Date: Thu, 11 Apr 2024 11:56:50 -0700 In-Reply-To: <20240126085444.324918-4-xiong.y.zhang@linux.intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240126085444.324918-1-xiong.y.zhang@linux.intel.com> <20240126085444.324918-4-xiong.y.zhang@linux.intel.com> Message-ID: Subject: Re: [RFC PATCH 03/41] perf: Set exclude_guest onto nmi_watchdog From: Sean Christopherson To: Xiong Zhang Cc: pbonzini@redhat.com, peterz@infradead.org, mizhang@google.com, kan.liang@intel.com, zhenyuw@linux.intel.com, dapeng1.mi@linux.intel.com, jmattson@google.com, kvm@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, zhiyuan.lv@intel.com, eranian@google.com, irogers@google.com, samantha.alt@intel.com, like.xu.linux@gmail.com, chao.gao@intel.com, Xiong Zhang Content-Type: text/plain; charset="us-ascii" On Fri, Jan 26, 2024, Xiong Zhang wrote: > From: Xiong Zhang > > The perf event for NMI watchdog is per cpu pinned system wide event, > if such event doesn't have exclude_guest flag, it will be put into > error state once guest with passthrough PMU starts, this breaks > NMI watchdog function totally. > > This commit adds exclude_guest flag for this perf event, so this perf > event is stopped during VM running, but it will continue working after > VM exit. In this way the NMI watchdog can not detect hardlockups during > VM running, it still breaks NMI watchdog function a bit. But host perf > event must be stopped during VM with passthrough PMU running, current > no other reliable method can be used to replace perf event for NMI > watchdog. As mentioned in the cover letter, I think this is backwards, and mediated PMU support should be disallowed if kernel-priority things like the watchdog are in use. Doubly so because this patch affects _everything_, not just systems with VMs that have a mediated PMU. > Signed-off-by: Xiong Zhang > Signed-off-by: Mingwei Zhang > --- > kernel/watchdog_perf.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c > index 8ea00c4a24b2..c8ba656ff674 100644 > --- a/kernel/watchdog_perf.c > +++ b/kernel/watchdog_perf.c > @@ -88,6 +88,7 @@ static struct perf_event_attr wd_hw_attr = { > .size = sizeof(struct perf_event_attr), > .pinned = 1, > .disabled = 1, > + .exclude_guest = 1, > }; > > /* Callback function for perf event subsystem */ > -- > 2.34.1 >