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a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1600622689; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ELUNMLCQYXoHQWzGjHTiBi/GvrgBrzUdsStDgdETjPA=; b=Ajg419VRwVNBaCnESvnWBGYX1dQ8DDFprO3wwe5+UvEno+/XgboH3A5bxhtY6hr785JAXL VPGuKWoChMzzg9BQ== To: Daniel Vetter Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends In-Reply-To: <20200920082353.GG438822@phenom.ffwll.local> References: <20200919091751.011116649@linutronix.de> <87pn6hc6g1.fsf@nanos.tec.linutronix.de> <20200920082353.GG438822@phenom.ffwll.local> Date: Sun, 20 Sep 2020 19:24:49 +0200 Message-ID: <87h7rscqe6.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200920_132456_944029_3C289F9F X-CRM114-Status: GOOD ( 18.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , Peter Zijlstra , Benjamin Herrenschmidt , Sebastian Andrzej Siewior , Joonas Lahtinen , dri-devel , linux-mips@vger.kernel.org, Ben Segall , Max Filippov , Guo Ren , sparclinux@vger.kernel.org, Vincent Chen , Will Deacon , Ard Biesheuvel , "open list:GENERIC INCLUDE/A..." , Vincent Guittot , Herbert Xu , Michael Ellerman , X86 ML , Russell King , linux-csky@vger.kernel.org, David Airlie , Mel Gorman , arcml , linux-xtensa@linux-xtensa.org, Paul McKenney , intel-gfx , linuxppc-dev , Steven Rostedt , Linus Torvalds , Jani Nikula , Rodrigo Vivi , Dietmar Eggemann , Linux ARM , Chris Zankel , Michal Simek , Thomas Bogendoerfer , Nick Hu , Linux-MM , Vineet Gupta , LKML , Arnd Bergmann , Daniel Vetter , Paul Mackerras , Andrew Morton , Daniel Bristot de Oliveira , "David S. Miller" , Greentime Hu Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sun, Sep 20 2020 at 10:23, Daniel Vetter wrote: > On Sun, Sep 20, 2020 at 08:23:26AM +0200, Thomas Gleixner wrote: >> On Sat, Sep 19 2020 at 12:37, Daniel Vetter wrote: >> > On Sat, Sep 19, 2020 at 12:35 PM Daniel Vetter wrote: >> >> I think it should be the case, but I want to double check: Will >> >> copy_*_user be allowed within a kmap_temporary section? This would >> >> allow us to ditch an absolute pile of slowpaths. >> > >> > (coffee just kicked in) copy_*_user is ofc allowed, but if you hit a >> > page fault you get a short read/write. This looks like it would remove >> > the need to handle these in a slowpath, since page faults can now be >> > served in this new kmap_temporary sections. But this sounds too good >> > to be true, so I'm wondering what I'm missing. >> >> In principle we could allow pagefaults, but not with the currently >> proposed interface which can be called from any context. Obviously if >> called from atomic context it can't handle user page faults. > > Yeah that's clear, but does the implemention need to disable pagefaults > unconditionally? As I wrote in the other reply it's not required and the final interface will neither disable preemption nor pagefaults (except for the atomic wrapper around it). Thanks, tglx _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel