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Fri, 17 Jul 2020 21:39:32 +0000 (UTC) IronPort-SDR: OnMnQZPTMqpriia/6aGOxZ8ofpnpk7P2POrXQDZTGiX/gWsfUGvBEmLrg1mzaLNMEgL2yRSUCu wBeFO1BjvTnA== X-IronPort-AV: E=McAfee;i="6000,8403,9685"; a="129247237" X-IronPort-AV: E=Sophos;i="5.75,364,1589266800"; d="scan'208";a="129247237" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2020 14:39:30 -0700 IronPort-SDR: AU7pg9gP52qGosMkjj44f+xwiuRZBXuNXBPORBl/nIscyOnQkujZOX7iJDcTIOdgYz9TXvt9wD p6bhZiX9j/bw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,364,1589266800"; d="scan'208";a="460984872" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by orsmga005.jf.intel.com with ESMTP; 17 Jul 2020 14:39:30 -0700 Date: Fri, 17 Jul 2020 14:39:30 -0700 From: Ira Weiny To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Fenghua Yu , x86@kernel.org, Dave Hansen , Dan Williams , Vishal Verma , Andrew Morton , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch Message-ID: <20200717213929.GR3008823@iweiny-DESK2.sc.intel.com> References: <20200717072056.73134-1-ira.weiny@intel.com> <20200717072056.73134-5-ira.weiny@intel.com> <20200717083140.GW10769@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200717083140.GW10769@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.11.1 (2018-12-01) X-Rspamd-Queue-Id: 40971180300C2 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 Fri, Jul 17, 2020 at 10:31:40AM +0200, Peter Zijlstra wrote: > On Fri, Jul 17, 2020 at 12:20:43AM -0700, ira.weiny@intel.com wrote: > > > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c > > index f362ce0d5ac0..d69250a7c1bf 100644 > > --- a/arch/x86/kernel/process.c > > +++ b/arch/x86/kernel/process.c > > @@ -42,6 +42,7 @@ > > #include > > #include > > #include > > +#include > > > > #include "process.h" > > > > @@ -184,6 +185,36 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp, > > return ret; > > } > > > > +/* > > + * NOTE: We wrap pks_init_task() and pks_sched_in() with > > + * CONFIG_ARCH_HAS_SUPERVISOR_PKEYS because using IS_ENABLED() fails > > + * due to the lack of task_struct->saved_pkrs in this configuration. > > + * Furthermore, we place them here because of the complexity introduced by > > + * header conflicts introduced to get the task_struct definition in the pkeys > > + * headers. > > + */ > > I don't see anything much useful in that comment. I'm happy to delete. Internal reviews questioned the motive here so I added the comment to inform why this style was chosen rather than the preferred IS_ENABLED(). I've deleted it now. > > > +#ifdef CONFIG_ARCH_HAS_SUPERVISOR_PKEYS > > +DECLARE_PER_CPU(u32, pkrs_cache); > > +static inline void pks_init_task(struct task_struct *tsk) > > +{ > > + /* New tasks get the most restrictive PKRS value */ > > + tsk->thread.saved_pkrs = INIT_PKRS_VALUE; > > +} > > +static inline void pks_sched_in(void) > > +{ > > + u64 current_pkrs = current->thread.saved_pkrs; > > + > > + /* Only update the MSR when current's pkrs is different from the MSR. */ > > + if (this_cpu_read(pkrs_cache) == current_pkrs) > > + return; > > + > > + write_pkrs(current_pkrs); > > Should we write that like: > > /* > * PKRS is only temporarily changed during specific code paths. > * Only a preemption during these windows away from the default > * value would require updating the MSR. > */ > if (unlikely(this_cpu_read(pkrs_cache) != current_pkrs)) > write_pkrs(current_pkrs); > > ? Yes I think the unlikely is better. Thanks, Ira > > > +} > > +#else > > +static inline void pks_init_task(struct task_struct *tsk) { } > > +static inline void pks_sched_in(void) { } > > +#endif