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Fri, 17 Jul 2020 08:31:45 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id A33083003D8; Fri, 17 Jul 2020 10:31:40 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9580929CF6F49; Fri, 17 Jul 2020 10:31:40 +0200 (CEST) Date: Fri, 17 Jul 2020 10:31:40 +0200 From: Peter Zijlstra To: ira.weiny@intel.com 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: <20200717083140.GW10769@hirez.programming.kicks-ass.net> References: <20200717072056.73134-1-ira.weiny@intel.com> <20200717072056.73134-5-ira.weiny@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200717072056.73134-5-ira.weiny@intel.com> X-Rspamd-Queue-Id: A3CFD41257 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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 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. > +#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); ? > +} > +#else > +static inline void pks_init_task(struct task_struct *tsk) { } > +static inline void pks_sched_in(void) { } > +#endif