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Christoph Müllner <christoph.muellner@vrull.eu> says: Currently, the Linux kernel suffers from a boot regression when running on the c906 QEMU emulation. Details have been reported here by Björn Töpel: https://lists.gnu.org/archive/html/qemu-devel/2024-01/msg04766.html The main issue is, that Linux enables XTheadMae for CPUs that have a T-Head mvendorid but QEMU maintainers don't want to emulate a CPU that uses reserved bits in PTEs. See also the following discussion for more context: https://lists.gnu.org/archive/html/qemu-devel/2024-02/msg00775.html This series renames "T-Head PBMT" to "MAE"/"XTheadMae" and only enables it if the th.sxstatus.MAEE bit is set. The th.sxstatus CSR is documented here: https://github.com/T-head-Semi/thead-extension-spec/blob/master/xtheadsxstatus.adoc XTheadMae is documented here: https://github.com/T-head-Semi/thead-extension-spec/blob/master/xtheadmae.adoc The QEMU patch to emulate th.sxstatus with the MAEE bit not set is here: https://lore.kernel.org/all/20240329120427.684677-1-christoph.muellner@vrull.eu/ After applying the referenced QEMU patch, this patchset allows to successfully boot a C906 QEMU system emulation ("-cpu thead-c906"). * b4-shazam-lts: riscv: T-Head: Test availability bit before enabling MAE errata riscv: thead: Rename T-Head PBMT to MAE Link: https://lore.kernel.org/r/20240407213236.2121592-1-christoph.muellner@vrull.eu Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com> |
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