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[109.43.177.59]) by smtp.gmail.com with ESMTPSA id t14-20020a05600c450e00b003e1fee8baacsm13959147wmo.25.2023.03.06.01.54.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Mar 2023 01:54:17 -0800 (PST) Message-ID: Date: Mon, 6 Mar 2023 10:54:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0 Subject: Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary Content-Language: en-US To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= Cc: qemu-devel@nongnu.org, Peter Maydell , Paolo Bonzini , Markus Armbruster , =?UTF-8?Q?Alex_Benn=c3=a9e?= , qemu-arm@nongnu.org, Maxim Levitsky , libvir-list@redhat.com, Richard Henderson , xen-devel@lists.xenproject.org, Reinoud Zandijk , Wilfred Mallawa , John Paul Adrian Glaubitz References: <20230306084658.29709-1-thuth@redhat.com> <20230306084658.29709-3-thuth@redhat.com> From: Thomas Huth In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.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, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, 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 06/03/2023 10.27, Daniel P. Berrangé wrote: > On Mon, Mar 06, 2023 at 09:46:55AM +0100, Thomas Huth wrote: >> Aside from not supporting KVM on 32-bit hosts, the qemu-system-x86_64 >> binary is a proper superset of the qemu-system-i386 binary. With the >> 32-bit host support being deprecated, it is now also possible to >> deprecate the qemu-system-i386 binary. >> >> With regards to 32-bit KVM support in the x86 Linux kernel, >> the developers confirmed that they do not need a recent >> qemu-system-i386 binary here: >> >> https://lore.kernel.org/kvm/Y%2ffkTs5ajFy0hP1U@google.com/ >> >> Reviewed-by: Daniel P. Berrangé >> Reviewed-by: Wilfred Mallawa >> Signed-off-by: Thomas Huth >> --- >> docs/about/deprecated.rst | 14 ++++++++++++++ >> 1 file changed, 14 insertions(+) >> >> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst >> index 1ca9dc33d6..c4fcc6b33c 100644 >> --- a/docs/about/deprecated.rst >> +++ b/docs/about/deprecated.rst >> @@ -34,6 +34,20 @@ deprecating the build option and no longer defend it in CI. The >> ``--enable-gcov`` build option remains for analysis test case >> coverage. >> >> +``qemu-system-i386`` binary (since 8.0) >> +''''''''''''''''''''''''''''''''''''''' >> + >> +The ``qemu-system-i386`` binary was mainly useful for running with KVM >> +on 32-bit x86 hosts, but most Linux distributions already removed their >> +support for 32-bit x86 kernels, so hardly anybody still needs this. The >> +``qemu-system-x86_64`` binary is a proper superset and can be used to >> +run 32-bit guests by selecting a 32-bit CPU model, including KVM support >> +on x86_64 hosts. Thus users are recommended to reconfigure their systems >> +to use the ``qemu-system-x86_64`` binary instead. If a 32-bit CPU guest >> +environment should be enforced, you can switch off the "long mode" CPU >> +flag, e.g. with ``-cpu max,lm=off``. > > I had the idea to check this today and this is not quite sufficient, > because we have code that changes the family/model/stepping for > 'max' which is target dependent: > > #ifdef TARGET_X86_64 > object_property_set_int(OBJECT(cpu), "family", 15, &error_abort); > object_property_set_int(OBJECT(cpu), "model", 107, &error_abort); > object_property_set_int(OBJECT(cpu), "stepping", 1, &error_abort); > #else > object_property_set_int(OBJECT(cpu), "family", 6, &error_abort); > object_property_set_int(OBJECT(cpu), "model", 6, &error_abort); > object_property_set_int(OBJECT(cpu), "stepping", 3, &error_abort); > #endif > > The former is a 64-bit AMD model and the latter is a 32-bit model. > > Seems LLVM was sensitive to this distinction to some extent: > > https://gitlab.com/qemu-project/qemu/-/issues/191 > > A further difference is that qemy-system-i686 does not appear to enable > the 'syscall' flag, but I've not figured out where that difference is > coming from in the code. Ugh, ok. I gave it a quick try with a patch like this: diff --git a/target/i386/cpu.c b/target/i386/cpu.c --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -4344,15 +4344,15 @@ static void max_x86_cpu_initfn(Object *obj) */ object_property_set_str(OBJECT(cpu), "vendor", CPUID_VENDOR_AMD, &error_abort); -#ifdef TARGET_X86_64 - object_property_set_int(OBJECT(cpu), "family", 15, &error_abort); - object_property_set_int(OBJECT(cpu), "model", 107, &error_abort); - object_property_set_int(OBJECT(cpu), "stepping", 1, &error_abort); -#else - object_property_set_int(OBJECT(cpu), "family", 6, &error_abort); - object_property_set_int(OBJECT(cpu), "model", 6, &error_abort); - object_property_set_int(OBJECT(cpu), "stepping", 3, &error_abort); -#endif + if (object_property_get_bool(obj, "lm", &error_abort)) { + object_property_set_int(obj, "family", 15, &error_abort); + object_property_set_int(obj, "model", 107, &error_abort); + object_property_set_int(obj, "stepping", 1, &error_abort); + } else { + object_property_set_int(obj, "family", 6, &error_abort); + object_property_set_int(obj, "model", 6, &error_abort); + object_property_set_int(obj, "stepping", 3, &error_abort); + } object_property_set_str(OBJECT(cpu), "model-id", "QEMU TCG CPU version " QEMU_HW_VERSION, &error_abort); ... but it seems like the "lm" property is not initialized there yet, so this does not work... :-/ Giving that we have soft-freeze tomorrow, let's ignore this patch for now and revisit this topic during the 8.1 cycle. But I'll queue the other 4 patches to get some pressure out of our CI during the freeze time. Thomas