[PATCH 6.6 08/50] MIPS: Always record SEGBITS in cpu_data.vmbits

Greg Kroah-Hartman
2026-04-13T16:15:00Z

From: Maciej W. Rozycki <macro@orcam.me.uk>

commit 8374c2cb83b95b3c92f129fd56527225c20a058c upstream.

With a 32-bit kernel running on 64-bit MIPS hardware the hardcoded value
of `cpu_vmbits' only records the size of compatibility useg and does not
reflect the size of native xuseg or the complete range of values allowed
in the VPN2 field of TLB entries.

An upcoming change will need the actual VPN2 value range permitted even
in 32-bit kernel configurations, so always include the `vmbits' member
in `struct cpuinfo_mips' and probe for SEGBITS when running on 64-bit
hardware and resorting to the currently hardcoded value of 31 on 32-bit
processors. No functional change for users of `cpu_vmbits'.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/mips/include/asm/cpu-features.h | 1 -
arch/mips/include/asm/cpu-info.h | 2 --
arch/mips/include/asm/mipsregs.h | 2 ++
arch/mips/kernel/cpu-probe.c | 13 ++++++++-----
arch/mips/kernel/cpu-r3k-probe.c | 2 ++
5 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/arch/mips/include/asm/cpu-features.h b/arch/mips/include/asm/cpu-features.h
index 404390bb87eaf..3f11e5218e6c6 100644
--- a/arch/mips/include/asm/cpu-features.h
+++ b/arch/mips/include/asm/cpu-features.h
@@ -484,7 +484,6 @@
# endif
# ifndef cpu_vmbits
# define cpu_vmbits cpu_data[0].vmbits
-# define __NEED_VMBITS_PROBE
# endif
#endif

diff --git a/arch/mips/include/asm/cpu-info.h b/arch/mips/include/asm/cpu-info.h
index a600670d00e97..1aee44124f118 100644
--- a/arch/mips/include/asm/cpu-info.h
+++ b/arch/mips/include/asm/cpu-info.h
@@ -80,9 +80,7 @@ struct cpuinfo_mips {
int srsets; /* Shadow register sets */
int package;/* physical package number */
unsigned int globalnumber;
-#ifdef CONFIG_64BIT
int vmbits; /* Virtual memory size in bits */
-#endif
void *data; /* Additional data */
unsigned int watch_reg_count; /* Number that exist */
unsigned int watch_reg_use_cnt; /* Usable by ptrace */
diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index e959a6b1a325c..92ad301395045 100644
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -1714,6 +1714,8 @@ do { \

#define read_c0_entryhi() __read_ulong_c0_register($10, 0)
#define write_c0_entryhi(val) __write_ulong_c0_register($10, 0, val)
+#define read_c0_entryhi_64() __read_64bit_c0_register($10, 0)
+#define write_c0_entryhi_64(val) __write_64bit_c0_register($10, 0, val)

#define read_c0_guestctl1() __read_32bit_c0_register($10, 4)
#define write_c0_guestctl1(val) __write_32bit_c0_register($10, 4, val)
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index c7fee72ea6067..d982bc3288eb7 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -208,11 +208,14 @@ static inline void set_elf_base_platform(const char *plat)

static inline void cpu_probe_vmbits(struct cpuinfo_mips *c)
{
-#ifdef __NEED_VMBITS_PROBE
- write_c0_entryhi(0x3fffffffffffe000ULL);
- back_to_back_c0_hazard();
- c->vmbits = fls64(read_c0_entryhi() & 0x3fffffffffffe000ULL);
-#endif
+ int vmbits = 31;
+
+ if (cpu_has_64bits) {
+ write_c0_entryhi_64(0x3fffffffffffe000ULL);
+ back_to_back_c0_hazard();
+ vmbits = fls64(read_c0_entryhi_64() & 0x3fffffffffffe000ULL);
+ }
+ c->vmbits = vmbits;
}

static void set_isa(struct cpuinfo_mips *c, unsigned int isa)
diff --git a/arch/mips/kernel/cpu-r3k-probe.c b/arch/mips/kernel/cpu-r3k-probe.c
index be93469c0e0ec..2adf95225aa7e 100644
--- a/arch/mips/kernel/cpu-r3k-probe.c
+++ b/arch/mips/kernel/cpu-r3k-probe.c
@@ -138,6 +138,8 @@ void cpu_probe(void)
else
cpu_set_nofpu_opts(c);

+ c->vmbits = 31;
+
reserve_exception_space(0, 0x400);
}

--
2.53.0