[PATCH 0/2] RISC-V: Test th.mxstatus.MAEE bit before enabling MAEE

From: "Christoph Müllner" <christoph.muellner@vrull.eu>
To: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Philipp Tomsich" <philipp.tomsich@vrull.eu>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Daniel Henrique Barboza" <dbarboza@ventanamicro.com>,
	"Heiko Stuebner" <heiko@sntech.de>,
	"Cooper Qu" <cooper.qu@linux.alibaba.com>,
	"Zhiwei Liu" <zhiwei_liu@linux.alibaba.com>,
	"Huang Tao" <eric.huang@linux.alibaba.com>,
	"Alistair Francis" <alistair.francis@wdc.com>,
	"Andrew Jones" <ajones@ventanamicro.com>,
	"Conor Dooley" <conor@kernel.org>
Cc: "Christoph Müllner" <christoph.muellner@vrull.eu>
Subject: [PATCH 0/2] RISC-V: Test th.mxstatus.MAEE bit before enabling MAEE
Date: Wed, 27 Mar 2024 11:31:28 +0100	[thread overview]
Message-ID: <20240327103130.3651950-1-christoph.muellner@vrull.eu> (raw)

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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