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Subject[PATCH 0/2] RISC-V: Test th.mxstatus.MAEE bit before enabling MAEE
Date
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 MAEE 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 "MAEE" and only enables it if
the th.mxstatus.MAEE bit is set.

Since th.mxstatus is only accessible in M-mode, this patch depends on
the following OpenSBI series:
http://lists.infradead.org/pipermail/opensbi/2024-March/006718.html

The th.mxstatus CSR is documented here:
https://github.com/T-head-Semi/thead-extension-spec/pull/45

The QEMU patch to emulate th.mxstatus with MAEE not set is here:
https://lists.gnu.org/archive/html/qemu-devel/2024-03/msg06368.html

After applying all referenced patchsets, this patchset allows to
successfully boot a C906 QEMU system emulation ("-cpu thead-c906").

Christoph Müllner (2):
riscv: thead: Rename T-Head PBMT to MAEE
riscv: T-Head: Test availability bit before enabling MAEE errata

arch/riscv/Kconfig.errata | 8 ++++----
arch/riscv/errata/thead/errata.c | 22 ++++++++++++++--------
arch/riscv/include/asm/errata_list.h | 20 ++++++++++----------
3 files changed, 28 insertions(+), 22 deletions(-)

--
2.44.0


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