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Fri, 13 Jun 2025 08:20:00 -0700 (PDT) Received: from [192.168.1.87] ([38.41.223.211]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2365deb87ddsm15534215ad.177.2025.06.13.08.20.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 13 Jun 2025 08:20:00 -0700 (PDT) Message-ID: <3743dd0d-0cfa-434a-ae19-54af637b1528@linaro.org> Date: Fri, 13 Jun 2025 08:19:59 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 0/7] Add additional plugin API functions to read and write memory and registers Content-Language: en-US To: Rowan Hart , qemu-devel@nongnu.org Cc: =?UTF-8?Q?Alex_Benn=C3=A9e?= , Paolo Bonzini , Richard Henderson , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Yanan Wang , Mahmoud Mandour , Marcel Apfelbaum , Alexandre Iooss , Zhao Liu , Eduardo Habkost References: <20250611232409.2936521-1-rowanbhart@gmail.com> From: Pierrick Bouvier In-Reply-To: <20250611232409.2936521-1-rowanbhart@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::634; envelope-from=pierrick.bouvier@linaro.org; helo=mail-pl1-x634.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 6/11/25 4:24 PM, Rowan Hart wrote: > This patch series adds several new API functions focused on enabling use > cases around reading and writing guest memory from QEMU plugins. To support > these new APIs, some utility functionality around retrieving information about > address spaces is added as well. > > The new qemu_plugin_write_register utilizes gdb_write_register, which is now > declared in gdbstub.h for this purpose instead of being static. > > qemu_plugin_write_memory_vaddr utilizes cpu_memory_rw_debug much the same as > the existing read_memory_vaddr function does. > > The read and write_hwaddr functions are the most different. These functions > use address_space_rw, which works well in most cases. There is an important > caveat that for writes, the page being written will be set dirty by the > write operation. This dirty setting requires locking the page range, > which can contend with an already held lock in page_collection_lock > when called in a tb translate callback with a write to the instruction > memory in the tb. The doc comments warn against doing this, and it's unlikely > anyone would want to do this. > > I've also added two test plugins: one that implements a simple hypercall > interface that guest code can use to communicate with the plugin in a > structured way with a test to ensure that this hypercall works and writing > virtual memory works. And one that implements a simple patch utility to patch > memory at runtime. The test for the second plugin ensures the patch applies > successfully to instruction memory, and can use both hw and vaddr methods. > > For v3, I've had a few comments from the last submission that I've addressed, > and some that I haven't for one reason or another: > > - Enforce QEMU_PLUGIN_CB_ flags in register read/write operations: done! > - Fix my commit messages and add long messages describing commits: done! > - Un-expose AS internals: done! Functions operate on current vCPU, current AS. > - Clean up use of current_cpu: done! > - Make functions take a vcpu_idx: not done. May revisit but it allows footguns. > Even for translation, seems best to not do this now. We can easily add _vcpu > versions of these functions in the future if we change our minds! > > For v5, I've just updated the enforcement of the QEMU_PLUGIN_CB_ flags to just > use immediate stores, which simplifies the implementation quite a lot and > should be more efficient too. Thanks Pierrick for the suggestion! > > v6 is a formatting pass, I left some whitespace that needed removal, some > license text was wrong, and so forth. > > v8 reverts a mistake I made extending the size of arrays of TCGHelperInfo > structs, as I misunderstood their sizes. It preserves adding an explicit > zero as the last entry for clarity, however. > > v9 fixes qemu_plugin_read_register to return -1 on parameter or flag state > error instead of 0. > > In v10, I relaxed the restriction on when the register r/w functions can be > called, allowing all them to be used from any callback where the CPU is not > currently executing, with additional notes in the documentation for exceptions > (atexit and flush, which do not operate on a specific CPU and in which > current_cpu is not set). > > v11 makes the cb flags functions inline and fixes a typo where cpu was asserted > but current_cpu was actually accessed. > > v12 removes the hypercalls plugin because the functions it tested are also > tested by the patcher plugin, making it redundant. We'll circle back on a > hypercalls API in the future as a part of the plugin API, not as a plugin > itself. > > Rowan Hart (1): > plugins: Add enforcement of QEMU_PLUGIN_CB flags in register R/W > callbacks > > novafacing (6): > gdbstub: Expose gdb_write_register function to consumers of gdbstub > plugins: Add register write API > plugins: Add memory virtual address write API > plugins: Add memory hardware address read/write API > plugins: Add patcher plugin and test > plugins: Update plugin version and add notes > > accel/tcg/plugin-gen.c | 30 +++ > gdbstub/gdbstub.c | 2 +- > include/exec/gdbstub.h | 14 ++ > include/hw/core/cpu.h | 1 + > include/qemu/plugin.h | 15 ++ > include/qemu/qemu-plugin.h | 176 ++++++++++++++-- > plugins/api.c | 135 +++++++++++- > plugins/core.c | 33 +++ > tests/tcg/Makefile.target | 1 + > tests/tcg/plugins/meson.build | 2 +- > tests/tcg/plugins/patch.c | 241 ++++++++++++++++++++++ > tests/tcg/x86_64/Makefile.softmmu-target | 32 ++- > tests/tcg/x86_64/system/patch-target.c | 27 +++ > tests/tcg/x86_64/system/validate-patch.py | 39 ++++ > 14 files changed, 725 insertions(+), 23 deletions(-) > create mode 100644 tests/tcg/plugins/patch.c > create mode 100644 tests/tcg/x86_64/system/patch-target.c > create mode 100755 tests/tcg/x86_64/system/validate-patch.py > @Alex, series looks good to me now. Would you like to add comments, or is it good for you also? Thanks, Pierrick