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Fri, 18 Dec 2020 15:33:06 +0000 (UTC) IronPort-SDR: fAWnniOvxJj3sLVRdL1mnMfjebv/GyJ1BL65RQEd8MeAkck3tUr7oPUS+qSPCqSL6wdO+S0evv B3LL5O0OYKWw== X-IronPort-AV: E=McAfee;i="6000,8403,9839"; a="172886317" X-IronPort-AV: E=Sophos;i="5.78,430,1599548400"; d="scan'208";a="172886317" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Dec 2020 07:33:04 -0800 IronPort-SDR: 6+CvPhIe2TEagrFVgsgicLDgQyHiU+2+stqbwXJUUMW48x8RU4e84m/J0bmxdRgC7c/SAs8XXy TZ+LCJpxLOow== X-IronPort-AV: E=Sophos;i="5.78,430,1599548400"; d="scan'208";a="414077191" Received: from nrojasva-mobl.amr.corp.intel.com (HELO [10.209.64.102]) ([10.209.64.102]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Dec 2020 07:33:03 -0800 Subject: Re: [NEEDS-REVIEW] [PATCH V3 04/10] x86/pks: Preserve the PKRS MSR on context switch To: Ira Weiny Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Peter Zijlstra , Dave Hansen , Fenghua Yu , x86@kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , linux-doc@vger.kernel.org, linux-nvdimm@lists.01.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Dan Williams , Greg KH References: <20201106232908.364581-1-ira.weiny@intel.com> <20201106232908.364581-5-ira.weiny@intel.com> <20201218041012.GC2506510@iweiny-DESK2.sc.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201218041012.GC2506510@iweiny-DESK2.sc.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/17/20 8:10 PM, Ira Weiny wrote: > On Thu, Dec 17, 2020 at 12:41:50PM -0800, Dave Hansen wrote: >> On 11/6/20 3:29 PM, ira.weiny@intel.com wrote: >>> void disable_TSC(void) >>> @@ -644,6 +668,8 @@ void __switch_to_xtra(struct task_struct *prev_p,= struct task_struct *next_p) >>> =20 >>> if ((tifp ^ tifn) & _TIF_SLD) >>> switch_to_sld(tifn); >>> + >>> + pks_sched_in(); >>> } >> >> Does the selftest for this ever actually schedule()? >=20 > At this point I'm not sure. This code has been in since the beginning.= So its > seen a lot of soak time. Think about it another way. Let's say this didn't get called on the first context switch away from the PKS-using task. Would anyone notice? How likely is this to happen? The function tracers or kprobes tend to be a great tool for this, at least for testing whether the code path you expect to hit is getting hit.