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On GICv2 and later, level triggered interrupts are pending when either the interrupt line is asserted or the interrupt was made pending by a GICD_ISPENDRn write. Making a level triggered interrupt pending by software persists until either the interrupt is acknowledged or cleared by writing GICD_ICPENDRn. As long as the interrupt line is asserted, the interrupt is pending in any case. This logic is transparently implemented in gic_test_pending() for GICv1 and GICv2. The function combines the "pending" irq_state flag (used for edge triggered interrupts and software requests) and the line status (tracked in the "level" field). However, we also incorrectly set the pending flag on a guest write to GICD_ISENABLERn if the line of a level triggered interrupt was asserted. This keeps the interrupt pending even if the line is de-asserted after some time. This incorrect logic is a leftover of the initial 11MPCore GIC implementation. That handles things slightly differently to the architected GICv1 and GICv2. The 11MPCore TRM does not give a lot of detail on the corner cases of its GIC's behaviour, and historically we have not wanted to investigate exactly what it does in reality, so QEMU's GIC model takes the approach of "retain our existing behaviour for 11MPCore, and implement the architectural standard for later GIC revisions". On that basis, commit 8d999995e45c10 in 2013 is where we added the "level-triggered interrupt with the line asserted" handling to gic_test_pending(), and we deliberately kept the old behaviour of gic_test_pending() for REV_11MPCORE. That commit should have added the "only if 11MPCore" condition to the setting of the pending bit on writes to GICD_ISENABLERn, but forgot it. Add the missing "if REV_11MPCORE" condition, so that our behaviour on GICv1 and GICv2 matches the GIC architecture requirements. Cc: qemu-stable@nongnu.org Fixes: 8d999995e45c10 ("arm_gic: Fix GIC pending behavior") Signed-off-by: Jan Klötzke <jan.kloetzke@kernkonzept.com> Message-id: 20240911114826.3558302-1-jan.kloetzke@kernkonzept.com Reviewed-by: Peter Maydell <peter.maydell@linaro.org> [PMM: expanded comment a little and converted to coding-style form; expanded commit message with the historical backstory] Signed-off-by: Peter Maydell <peter.maydell@linaro.org> (cherry picked from commit 110684c9a69a02cbabfbddcd3afa921826ad565c) Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
=========== QEMU README =========== QEMU is a generic and open source machine & userspace emulator and virtualizer. QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board). QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation. QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager. QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file. Documentation ============= Documentation can be found hosted online at `<https://www.qemu.org/documentation/>`_. The documentation for the current development version that is available at `<https://www.qemu.org/docs/master/>`_ is generated from the ``docs/`` folder in the source tree, and is built by `Sphinx <https://www.sphinx-doc.org/en/master/>`_. Building ======== QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are: .. code-block:: shell mkdir build cd build ../configure make Additional information can also be found online via the QEMU website: * `<https://wiki.qemu.org/Hosts/Linux>`_ * `<https://wiki.qemu.org/Hosts/Mac>`_ * `<https://wiki.qemu.org/Hosts/W32>`_ Submitting patches ================== The QEMU source code is maintained under the GIT version control system. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu.git When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the `style section <https://www.qemu.org/docs/master/devel/style.html>`_ of the Developers Guide. Additional information on submitting patches can be found online via the QEMU website * `<https://wiki.qemu.org/Contribute/SubmitAPatch>`_ * `<https://wiki.qemu.org/Contribute/TrivialPatches>`_ The QEMU website is also maintained under source control. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu-web.git * `<https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/>`_ A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once. For installation instructions, please go to * `<https://github.com/stefanha/git-publish>`_ The workflow with 'git-publish' is: .. code-block:: shell $ git checkout master -b my-feature $ # work on new commits, add your 'Signed-off-by' lines to each $ git publish Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future. Sending v2: .. code-block:: shell $ git checkout my-feature # same topic branch $ # making changes to the commits (using 'git rebase', for example) $ git publish Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2. Bug reporting ============= The QEMU project uses GitLab issues to track bugs. Bugs found when running code built from QEMU git or upstream released sources should be reported via: * `<https://gitlab.com/qemu-project/qemu/-/issues>`_ If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via GitLab. For additional information on bug reporting consult: * `<https://wiki.qemu.org/Contribute/ReportABug>`_ ChangeLog ========= For version history and release notes, please visit `<https://wiki.qemu.org/ChangeLog/>`_ or look at the git history for more detailed information. Contact ======= The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC * `<mailto:qemu-devel@nongnu.org>`_ * `<https://lists.nongnu.org/mailman/listinfo/qemu-devel>`_ * #qemu on irc.oftc.net Information on additional methods of contacting the community can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/StartHere>`_