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Merge patch series "RISC-V: Test th.sxstatus.MAEE bit before enabling MAEE"

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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>
This commit is contained in:
Palmer Dabbelt 2024-04-25 10:22:36 -07:00
commit 6beb6bc5a8
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GPG Key ID: 2E1319F35FBB1889
3 changed files with 29 additions and 23 deletions
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8
arch/riscv/Kconfig.errata
View File

@ -82,14 +82,14 @@ config ERRATA_THEAD
Otherwise, please say "N" here to avoid unnecessary overhead.
config ERRATA_THEAD_PBMT
bool "Apply T-Head memory type errata"
config ERRATA_THEAD_MAE
bool "Apply T-Head's memory attribute extension (XTheadMae) errata"
depends on ERRATA_THEAD && 64BIT && MMU
select RISCV_ALTERNATIVE_EARLY
default y
help
This will apply the memory type errata to handle the non-standard
memory type bits in page-table-entries on T-Head SoCs.
This will apply the memory attribute extension errata to handle the
non-standard PTE utilization on T-Head SoCs (XTheadMae).
If you don't know what to do here, say "Y".

24
arch/riscv/errata/thead/errata.c
View File

@ -19,20 +19,26 @@
#include <asm/patch.h>
#include <asm/vendorid_list.h>
static bool errata_probe_pbmt(unsigned int stage,
unsigned long arch_id, unsigned long impid)
#define CSR_TH_SXSTATUS 0x5c0
#define SXSTATUS_MAEE _AC(0x200000, UL)
static bool errata_probe_mae(unsigned int stage,
unsigned long arch_id, unsigned long impid)
{
if (!IS_ENABLED(CONFIG_ERRATA_THEAD_PBMT))
if (!IS_ENABLED(CONFIG_ERRATA_THEAD_MAE))
return false;
if (arch_id != 0 || impid != 0)
return false;
if (stage == RISCV_ALTERNATIVES_EARLY_BOOT ||
stage == RISCV_ALTERNATIVES_MODULE)
return true;
if (stage != RISCV_ALTERNATIVES_EARLY_BOOT &&
stage != RISCV_ALTERNATIVES_MODULE)
return false;
return false;
if (!(csr_read(CSR_TH_SXSTATUS) & SXSTATUS_MAEE))
return false;
return true;
}
/*
@ -140,8 +146,8 @@ static u32 thead_errata_probe(unsigned int stage,
{
u32 cpu_req_errata = 0;
if (errata_probe_pbmt(stage, archid, impid))
cpu_req_errata |= BIT(ERRATA_THEAD_PBMT);
if (errata_probe_mae(stage, archid, impid))
cpu_req_errata |= BIT(ERRATA_THEAD_MAE);
errata_probe_cmo(stage, archid, impid);

20
arch/riscv/include/asm/errata_list.h
View File

@ -23,7 +23,7 @@
#endif
#ifdef CONFIG_ERRATA_THEAD
#define ERRATA_THEAD_PBMT 0
#define ERRATA_THEAD_MAE 0
#define ERRATA_THEAD_PMU 1
#define ERRATA_THEAD_NUMBER 2
#endif
@ -53,20 +53,20 @@ asm(ALTERNATIVE("sfence.vma %0", "sfence.vma", SIFIVE_VENDOR_ID, \
* in the default case.
*/
#define ALT_SVPBMT_SHIFT 61
#define ALT_THEAD_PBMT_SHIFT 59
#define ALT_THEAD_MAE_SHIFT 59
#define ALT_SVPBMT(_val, prot) \
asm(ALTERNATIVE_2("li %0, 0\t\nnop", \
"li %0, %1\t\nslli %0,%0,%3", 0, \
RISCV_ISA_EXT_SVPBMT, CONFIG_RISCV_ISA_SVPBMT, \
"li %0, %2\t\nslli %0,%0,%4", THEAD_VENDOR_ID, \
ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT) \
ERRATA_THEAD_MAE, CONFIG_ERRATA_THEAD_MAE) \
: "=r"(_val) \
: "I"(prot##_SVPBMT >> ALT_SVPBMT_SHIFT), \
"I"(prot##_THEAD >> ALT_THEAD_PBMT_SHIFT), \
"I"(prot##_THEAD >> ALT_THEAD_MAE_SHIFT), \
"I"(ALT_SVPBMT_SHIFT), \
"I"(ALT_THEAD_PBMT_SHIFT))
"I"(ALT_THEAD_MAE_SHIFT))
#ifdef CONFIG_ERRATA_THEAD_PBMT
#ifdef CONFIG_ERRATA_THEAD_MAE
/*
* IO/NOCACHE memory types are handled together with svpbmt,
* so on T-Head chips, check if no other memory type is set,
@ -83,11 +83,11 @@ asm volatile(ALTERNATIVE( \
"slli t3, t3, %3\n\t" \
"or %0, %0, t3\n\t" \
"2:", THEAD_VENDOR_ID, \
ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT) \
ERRATA_THEAD_MAE, CONFIG_ERRATA_THEAD_MAE) \
: "+r"(_val) \
: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT), \
"I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT), \
"I"(ALT_THEAD_PBMT_SHIFT) \
: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_MAE_SHIFT), \
"I"(_PAGE_PMA_THEAD >> ALT_THEAD_MAE_SHIFT), \
"I"(ALT_THEAD_MAE_SHIFT) \
: "t3")
#else
#define ALT_THEAD_PMA(_val)