linux-kernel - RE: [RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export pt_get_curr

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <DS0PR11MB6373C84139621DC447D3F466DC4E9@DS0PR11MB6373.namprd11.prod.outlook.com>
Date:   Thu, 22 Sep 2022 12:58:49 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>,
        "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        "Namhyung Kim" <namhyung@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
CC:     "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export
 pt_get_curr_event()

On Thursday, September 22, 2022 8:34 PM, Liang, Kan wrote:
> > To solve the problem, introduce and export pt_get_curr_event() for KVM
> > to get current pt event.
> 
> I don't think the current pt event is created by KVM. IIUC, the patch basically
> expose the event created by the other user to KVM. That doesn't sounds
> correct.

Yes, that's the host PT event running on the current CPU. Not created by KVM.

> 
> I think it should be perf's responsibility to decide which events should be
> disabled, and which MSRs should be switched. Because only perf can see all the
> events. The users should only see the events they created.

For other pmu cases, yes. For PT, its management is simpler than other pmu
resources and PT PMU is much simpler. It doesn't have a scheduler to manage
events.

I think the usage here is similar to the CPU thread scheduling case. When we have
CPUs isolated from the CPU scheduler, i.e. no scheduler for those CPUs, basically
we rely on users to ping tasks to those CPUs (e.g. taskset).

For the commit log, probably we don't need those KVM details here. Simplify a bit:

Add a function to expose the current running PT event to users. One usage is in KVM,
it needs to get and disable the running host PT event before VMEnter to the guest and
resumes the event after VMexit to host.