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Wed, 05 May 2021 18:02:37 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id BB46861176; Wed, 5 May 2021 18:02:33 +0000 (UTC) Date: Wed, 5 May 2021 19:02:31 +0100 From: Catalin Marinas To: Will Deacon Cc: Vikram Sethi , Alex Williamson , Mark Kettenis , Marc Zyngier , Shanker Donthineni , "christoffer.dall@arm.com" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.cs.columbia.edu" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , Jason Sequeira Subject: Re: [RFC 1/2] vfio/pci: keep the prefetchable attribute of a BAR region in VMA Message-ID: <20210505180228.GA3874@arm.com> References: <878s4zokll.wl-maz@kernel.org> <87eeeqvm1d.wl-maz@kernel.org> <87bl9sunnw.wl-maz@kernel.org> <20210503084432.75e0126d@x1.home.shazbot.org> <20210504083005.GA12290@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210504083005.GA12290@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210505_110236_258135_39F7DAC5 X-CRM114-Status: GOOD ( 13.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Tue, May 04, 2021 at 09:30:05AM +0100, Will Deacon wrote: > On Mon, May 03, 2021 at 10:03:59PM +0000, Vikram Sethi wrote: > > Will/Catalin, perhaps you could explain your thought process on why you chose > > Normal NC for ioremap_wc on the armv8 linux port instead of Device GRE or other > > Device Gxx. > > I think a combination of: compatibility with 32-bit Arm, the need to > support unaligned accesses and the potential for higher performance. IIRC the _wc suffix also matches the pgprot_writecombine() used by some drivers to map a video framebuffer into user space. Accesses to the framebuffer are not guaranteed to be aligned (memset/memcpy don't ensure alignment on arm64 and the user doesn't have a memset_io or memcpy_toio). > Furthermore, ioremap() already gives you a Device memory type, and we're > tight on MAIR space. We have MT_DEVICE_GRE currently reserved though no in-kernel user, we might as well remove it. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel