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Tue, 14 Jul 2020 19:29:32 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id AA08A9817E0; Tue, 14 Jul 2020 21:29:30 +0200 (CEST) Date: Tue, 14 Jul 2020 21:29:30 +0200 From: Peter Zijlstra To: Ira Weiny Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , x86@kernel.org, Dave Hansen , Dan Williams , Vishal Verma , Andrew Morton , Fenghua Yu , 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: [RFC PATCH 12/15] kmap: Add stray write protection for device pages Message-ID: <20200714192930.GH5523@worktop.programming.kicks-ass.net> References: <20200714070220.3500839-1-ira.weiny@intel.com> <20200714070220.3500839-13-ira.weiny@intel.com> <20200714084451.GQ10769@hirez.programming.kicks-ass.net> <20200714190615.GC3008823@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200714190615.GC3008823@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: 6458A18229835 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 Tue, Jul 14, 2020 at 12:06:16PM -0700, Ira Weiny wrote: > On Tue, Jul 14, 2020 at 10:44:51AM +0200, Peter Zijlstra wrote: > > So, if I followed along correctly, you're proposing to do a WRMSR per > > k{,un}map{_atomic}(), sounds like excellent performance all-round :-( > > Only to pages which have this additional protection, ie not DRAM. > > User mappings of this memory is not affected (would be covered by User PKeys if > desired). User mappings to persistent memory are the primary use case and the > performant path. Because performance to non-volatile memory doesn't matter? I think Dave has a better answer here ...