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Message-ID: Date: Wed, 15 Apr 2020 17:11:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200415_091156_338370_0625899B X-CRM114-Status: GOOD ( 19.87 ) 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: kvm@vger.kernel.org, Raphael Gault , Julien Thierry , Will Deacon , kvmarm , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 15/04/2020 16:55, Ard Biesheuvel wrote: > On Wed, 15 Apr 2020 at 17:43, Ard Biesheuvel wrote: >> >> On Tue, 7 Apr 2020 at 17:15, Alexandru Elisei wrote: >>> >>> Hi, >>> >>> I've tested this patch by running badblocks and fio on a flash device inside a >>> guest, everything worked as expected. >>> >>> I've also looked at the flowcharts for device operation from Intel Application >>> Note 646, pages 12-21, and they seem implemented correctly. >>> >>> A few minor issues below. >>> >>> On 2/21/20 4:55 PM, Andre Przywara wrote: >>>> From: Raphael Gault >>>> >>>> The EDK II UEFI firmware implementation requires some storage for the EFI >>>> variables, which is typically some flash storage. >>>> Since this is already supported on the EDK II side, we add a CFI flash >>>> emulation to kvmtool. >>>> This is backed by a file, specified via the --flash or -F command line >>>> option. Any flash writes done by the guest will immediately be reflected >>>> into this file (kvmtool mmap's the file). >>>> The flash will be limited to the nearest power-of-2 size, so only the >>>> first 2 MB of a 3 MB file will be used. >>>> >>>> This implements a CFI flash using the "Intel/Sharp extended command >>>> set", as specified in: >>>> - JEDEC JESD68.01 >>>> - JEDEC JEP137B >>>> - Intel Application Note 646 >>>> Some gaps in those specs have been filled by looking at real devices and >>>> other implementations (QEMU, Linux kernel driver). >>>> >>>> At the moment this relies on DT to advertise the base address of the >>>> flash memory (mapped into the MMIO address space) and is only enabled >>>> for ARM/ARM64. The emulation itself is architecture agnostic, though. >>>> >>>> This is one missing piece toward a working UEFI boot with kvmtool on >>>> ARM guests, the other is to provide writable PCI BARs, which is WIP. >>>> >> >> I have given this a spin with UEFI built for kvmtool, and it appears >> to be working correctly. However, I noticed that it is intolerably >> slow, which seems to be caused by the fact that both array mode and >> command mode (or whatever it is called in the CFI spec) are fully >> emulated, whereas in the QEMU implementation (for instance), the >> region is actually exposed to the guest using a read-only KVM memslot >> in array mode, and so the read accesses are made natively. >> >> It is also causing problems in the UEFI implementation, as we can no >> longer use unaligned accesses to read from the region, which is >> something the code currently relies on (and which works fine on actual >> hardware as long as you use normal non-cacheable mappings) >> > > Actually, the issue is not alignment. The issue is with instructions > with multiple outputs, which means you cannot do an ordinary memcpy() > from the NOR region using ldp instructions, aligned or not. Yes, we traced that down to an "ldrb with post-inc", in the memcpy code. My suggestion was to provide a version of memcpy_{from,to}_io(), as Linux does, which only uses MMIO accessors to avoid "fancy" instructions. Back at this point I was challenging the idea of accessing a flash device with a normal memory mapping, because of it failing when being in some query mode. Do you know of any best practices for flash mappings? Are two mappings common? Cheers, Andre _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel