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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4606f2c473bsm39144773f8f.28.2026.06.15.07.48.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jun 2026 07:48:35 -0700 (PDT) Date: Mon, 15 Jun 2026 10:48:31 -0400 From: "Michael S. Tsirkin" To: Peter Maydell Cc: Gavin Shan , qemu-arm@nongnu.org, qemu-devel@nongnu.org, peterx@redhat.com, alex@shazbot.org, richard.henderson@linaro.org, berrange@redhat.com, philmd@oss.qualcomm.com, philmd@mailo.com, david@kernel.org, clg@redhat.com, pbonzini@redhat.com, phrdina@redhat.com, jugraham@redhat.com, liugang24219@sangfor.com.cn, dinghui@sangfor.com.cn, shan.gavin@gmail.com Subject: Re: [PATCH v2 1/2] system/memory: Use qemu_ram_{copy, move}() in ram device region accessors Message-ID: <20260615104646-mutt-send-email-mst@kernel.org> References: <20260615100200.266968-1-gshan@redhat.com> <20260615100200.266968-2-gshan@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: zN9vcfIlk11S2qPsU5WJ-D0c3gvjXROtEGrl0WXrobM_1781534916 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Mon, Jun 15, 2026 at 11:57:09AM +0100, Peter Maydell wrote: > On Mon, 15 Jun 2026 at 11:03, Gavin Shan wrote: > > > > All ram device regions were turned to be indirectly accessible by commit > > 4a2e242bbb ("memory: Don't use memcpy for ram_device regions"). This leads > > to guest hang on attempt to build 'cuda-samples' as reported by Julia. The > > guest is started by the following command lines, with GH100 GPU card passed > > from the host. > > > diff --git a/include/system/memory.h b/include/system/memory.h > > index 1417132f6d..5878727d09 100644 > > --- a/include/system/memory.h > > +++ b/include/system/memory.h > > @@ -2897,6 +2897,8 @@ void address_space_register_map_client(AddressSpace *as, QEMUBH *bh); > > void address_space_unregister_map_client(AddressSpace *as, QEMUBH *bh); > > > > /* Internal functions, part of the implementation of address_space_read. */ > > +void qemu_ram_copy(void *dest, const void *src, size_t n); > > +void qemu_ram_move(void *dest, const void *src, size_t n); > > New function prototypes in include headers need documentation comments. > > In particular for these, it's really important that we clearly say > what semantics we are attempting to provide with them, so that > (a) when we're reviewing or later updating the implementation we > know what we are trying to provide > (b) when we're looking at the callsites we know what the function > is guaranteeing to us and what it is not, and thus whether it's > OK to use it or we need something els. > > > +#if defined(__i386__) || defined(__x86_64__) > > +#define HOST_UNALIGNED_MMIO_OK 1 > > +#else > > +#define HOST_UNALIGNED_MMIO_OK 0 > > +#endif > > We need to do something better than this. We can't > just say "oh, we trust that on x86 this works": it is > neither actually true that the compiler guarantees it even > on x86, nor is it the case that only x86 can do unaligned > accesses to normal RAM. > > thanks > -- PMM Why normal RAM? It explicitly says MMIO. x86 seems to be the only arch that can do unaligned MMIO?