[PATCH 2/3] riscv: cpufeature: Add ISA extension parsing for Supm

[Guodong Xu]

Supm has been ratified in the RISC-V Pointer Masking specification
(Version 1.0, 10/2024) and is mandated in RVA23 Profiles (Version 1.0,
2024-10-17) for RVA23U64. Supm indicates userspace pointer masking
support.

Remove the previous macro aliasing of Supm to Ssnpm/Smnpm in hwcap.h,
treating Supm as a distinct RISC-V ISA extension ID.

Add ISA parsing logic for Supm, and implement a validator to ensure
that Supm is only reported as available if Kconfig allows it and the
underlying Ssnpm (for supervisor mode) or Smnpm (for machine mode)
extension is present. Supm relies on Ssnpm or Smnpm to provide the
underlying hardware implementation.

With this change, "supm" will be reported (when available) in
/proc/cpuinfo as part of the "isa" and "hart isa" string.

Link: https://lore.kernel.org/lkml/20260101-legume-engraved-0fae8282cfbe@spud/#r [1]
Link: https://lore.kernel.org/all/4ebbe14b-2579-4ba6-808d-d50c24641d04@sifive.com/#r [2]
Signed-off-by: Guodong Xu <guodong at riscstar.com>
---
 arch/riscv/include/asm/hwcap.h |  3 +--
 arch/riscv/kernel/cpufeature.c | 35 +++++++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 4369a2338541..7653e5cff9ae 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -110,6 +110,7 @@
 #define RISCV_ISA_EXT_ZALASR		101
 #define RISCV_ISA_EXT_ZILSD		102
 #define RISCV_ISA_EXT_ZCLSD		103
+#define RISCV_ISA_EXT_SUPM		104
 
 #define RISCV_ISA_EXT_XLINUXENVCFG	127
 
@@ -118,10 +119,8 @@
 
 #ifdef CONFIG_RISCV_M_MODE
 #define RISCV_ISA_EXT_SxAIA		RISCV_ISA_EXT_SMAIA
-#define RISCV_ISA_EXT_SUPM		RISCV_ISA_EXT_SMNPM
 #else
 #define RISCV_ISA_EXT_SxAIA		RISCV_ISA_EXT_SSAIA
-#define RISCV_ISA_EXT_SUPM		RISCV_ISA_EXT_SSNPM
 #endif
 
 #endif /* _ASM_RISCV_HWCAP_H */
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index fa591aff9d33..39680280f858 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -296,6 +296,27 @@ static int riscv_ext_svadu_validate(const struct riscv_isa_ext_data *data,
 	return 0;
 }
 
+static int riscv_ext_supm_validate(const struct riscv_isa_ext_data *data,
+				   const unsigned long *isa_bitmap)
+{
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_SUPM))
+		return -EINVAL;
+
+	/*
+	 * Supm requires Ssnpm for S-mode or Smnpm for M-mode to provide
+	 * pointer masking for the U-mode execution environment.
+	 */
+	if (IS_ENABLED(CONFIG_RISCV_M_MODE)) {
+		if (__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_SMNPM))
+			return 0;
+	} else {
+		if (__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_SSNPM))
+			return 0;
+	}
+
+	return -EPROBE_DEFER;
+}
+
 static const unsigned int riscv_a_exts[] = {
 	RISCV_ISA_EXT_ZAAMO,
 	RISCV_ISA_EXT_ZALRSC,
@@ -429,6 +450,15 @@ static const unsigned int riscv_c_exts[] = {
 	RISCV_ISA_EXT_ZCD,
 };
 
+/*
+ * Smnpm and Ssnpm provide pointer masking for the next lower privilege mode
+ * (U-mode), thus enabling Supm. Both extensions imply the same subset.
+ */
+static const unsigned int riscv_supm_exts[] = {
+	RISCV_ISA_EXT_XLINUXENVCFG,
+	RISCV_ISA_EXT_SUPM
+};
+
 /*
  * The canonical order of ISA extension names in the ISA string is defined in
  * chapter 27 of the unprivileged specification.
@@ -552,12 +582,13 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
 	__RISCV_ISA_EXT_DATA_VALIDATE(zvkt, RISCV_ISA_EXT_ZVKT, riscv_ext_vector_crypto_validate),
 	__RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
 	__RISCV_ISA_EXT_DATA(smmpm, RISCV_ISA_EXT_SMMPM),
-	__RISCV_ISA_EXT_SUPERSET(smnpm, RISCV_ISA_EXT_SMNPM, riscv_xlinuxenvcfg_exts),
+	__RISCV_ISA_EXT_SUPERSET(smnpm, RISCV_ISA_EXT_SMNPM, riscv_supm_exts),
 	__RISCV_ISA_EXT_DATA(smstateen, RISCV_ISA_EXT_SMSTATEEN),
 	__RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
 	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
-	__RISCV_ISA_EXT_SUPERSET(ssnpm, RISCV_ISA_EXT_SSNPM, riscv_xlinuxenvcfg_exts),
+	__RISCV_ISA_EXT_SUPERSET(ssnpm, RISCV_ISA_EXT_SSNPM, riscv_supm_exts),
 	__RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
+	__RISCV_ISA_EXT_DATA_VALIDATE(supm, RISCV_ISA_EXT_SUPM, riscv_ext_supm_validate),
 	__RISCV_ISA_EXT_DATA(svade, RISCV_ISA_EXT_SVADE),
 	__RISCV_ISA_EXT_DATA_VALIDATE(svadu, RISCV_ISA_EXT_SVADU, riscv_ext_svadu_validate),
 	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),

-- 
2.43.0