[PATCH v2 4/6] riscv: hwprobe: Report Supm only when available

[Radim Krčmář]

The RISC-V ISA defines Supm as

  "An extension that indicates that there is pointer-masking support
  available in user mode, with some facility provided in the application
  execution environment to control pointer masking."

Our facility, PR_{SET,GET}_TAGGED_ADDR_CTRL, always returns -EINVAL
unless CONFIG_RISCV_ISA_SUPM is enabled, Supm is present on all harts,
and the user-mode is running in 64-bit mode.

While we technically could advertise Supm even when it only supports
PMLEN=0, it seems a bit more useful to report Supm only in cases where
the userspace can configure non-zero pointer masking.
A minor downside of this approach is that we'll need to update the Supm
detection line when more pointer-masking modes get added.

hwprobe currently reports Supm from the per-hart ISA bitmaps alone, so
it can advertise Supm when the facility always returns -EINVAL.
Report slightly more precise environment to user-mode.

Hiding Supm in compat tasks would add complexity that doesn't seem
justified as 32-bit code has no reason to look at Supm anyway.
Reporting based on the global sysctl toggle isn't done either.

Fixes: 3c2e0aff7b4f ("riscv: hwprobe: Export the Supm ISA extension")
Signed-off-by: Radim Krčmář <radim.krcmar at oss.qualcomm.com>
---
v2:
* Used pmlen helpers from v7.4-rc1 [Guodong]
* Updated commit message to reflect the reasoning
---
 arch/riscv/kernel/sys_hwprobe.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index a9aa1e193840..21738e2539a8 100644
--- a/arch/riscv/kernel/sys_hwprobe.c
+++ b/arch/riscv/kernel/sys_hwprobe.c
@@ -101,6 +101,9 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
 	if (is_user_lpad_enabled())
 		pair->value |= RISCV_HWPROBE_EXT_ZICFILP;
 
+	if (riscv_have_user_pmlen(7) || riscv_have_user_pmlen(16))
+		pair->value |= RISCV_HWPROBE_EXT_SUPM;
+
 	/*
 	 * Loop through and record extensions that 1) anyone has, and 2) anyone
 	 * doesn't have.
@@ -183,9 +186,6 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
 			EXT_KEY(isainfo->isa, ZFH, pair->value, missing);
 			EXT_KEY(isainfo->isa, ZFHMIN, pair->value, missing);
 		}
-
-		if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM))
-			EXT_KEY(isainfo->isa, SUPM, pair->value, missing);
 	}
 
 	/* Now turn off reporting features if any CPU is missing it. */
-- 
2.55.0