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[128.197.127.33]) by smtp.gmail.com with ESMTPSA id x8-20020ac87008000000b003bfb6ddc49dsm1385339qtm.1.2023.03.10.05.02.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Mar 2023 05:02:49 -0800 (PST) Date: Fri, 10 Mar 2023 08:02:45 -0500 From: Alexander Bulekov To: Peter Maydell Cc: Fiona Ebner , qemu-devel@nongnu.org, Stefan Hajnoczi , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Mauro Matteo Cascella , Peter Xu , Jason Wang , David Hildenbrand , Gerd Hoffmann , Thomas Huth , Laurent Vivier , Bandan Das , "Edgar E . Iglesias" , Darren Kenny , Bin Meng , Paolo Bonzini , "Michael S . Tsirkin" , Marcel Apfelbaum , Daniel P =?utf-8?B?LiBCZXJyYW5nw6k=?= , Eduardo Habkost , Jon Maloy , Siqi Chen , Fam Zheng Subject: Re: [PATCH v6 1/4] memory: prevent dma-reentracy issues Message-ID: <20230310130245.oyjdeihisuvgl6rz@mozz.bu.edu> References: <20230205040737.3567731-1-alxndr@bu.edu> <20230205040737.3567731-2-alxndr@bu.edu> <9cfa0cc8-01c7-cf79-72ef-3224d1276e16@proxmox.com> <20230310122347.hghmijad7wajiqne@mozz.bu.edu> <20230310123117.d2uxze7zqtigmg44@mozz.bu.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CES-GSUITE_AUTH: bf3aNvsZpxl8 Received-SPF: pass client-ip=216.71.137.80; envelope-from=alxndr@bu.edu; helo=esa7.hc2706-39.iphmx.com X-Spam_score_int: 0 X-Spam_score: -0.1 X-Spam_bar: / X-Spam_report: (-0.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, HK_RANDOM_ENVFROM=0.999, HK_RANDOM_FROM=1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@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-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 230310 1245, Peter Maydell wrote: > On Fri, 10 Mar 2023 at 12:32, Alexander Bulekov wrote: > > This MR seems to be "lsi-ram". > > > > From hw/scsi/lsi53c895a.c: > > > > memory_region_init_io(&s->ram_io, OBJECT(s), &lsi_ram_ops, s, > > "lsi-ram", 0x2000); > > > > So the LSI device is reading an LSI "Script" from its own IO region.. In > > this particular case, I think there was no reason to use > > memory_region_init_io rather than memory_region_init_ram, but this makes > > me worried that there are other devices that use something like this. > > This particular device predates the entire MemoryRegion set of > abstractions, so it might have seemed easier at the time. > The endianness handling of the current code is also a bit > confusing and might make it tricky to convert to a RAM MR. With my trivial mr_io - > mr_ram conversion, I no longer hit the re-entrancy tracepoint, and my livecd boots, but it's probably not exhaustively using the script functionality.. Does the endianness actually cause a problem? As long as all accesses (CPU -> LSI_RAM and LSI -> LSI_RAM) occur through the address_space API, are we safe? -Alex