[PATCH v3 1/3] riscv: hwprobe: initialize pair->value in hwprobe_one_pair()

[Andy Chiu]

The vendor-extension handlers reached from hwprobe_one_pair()
(hwprobe_isa_vendor_ext_thead_0() and friends) only OR the present bits
into pair->value via VENDOR_EXTENSION_SUPPORTED() and clear their own
missing bits; they assume the caller has already zeroed pair->value.

That holds for hwprobe_get_values() (it zeroes each pair) and
hwprobe_get_cpus() (it re-initializes its scratch pair per key), but not
for complete_hwprobe_vdso_data(), which reuses a single pair across all
keys without re-zeroing. A vendor key therefore inherits stale bits from
the previously probed key, and the wrong value is cached in the vDSO
all_cpu_hwprobe_values[] and handed to userspace on the fast patih.

Zero pair->value once at the top of hwprobe_one_pair() so every handler
starts from a clean value regardless of the caller, and drop the now
redundant zeroing in the *_BLOCK_SIZE cases. hwprobe_isa_ext0() keeps its
own zeroing because hwprobe_ext0_has() calls it directly, bypassing
hwprobe_one_pair().

Fixes: a5ea53da65c5 ("riscv: hwprobe: Add thead vendor extension probing")
Signed-off-by: Andy Chiu <tchiu at tenstorrent.com>
---
Changelog v3:
 - new patch since v3
---
 arch/riscv/kernel/sys_hwprobe.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index caf6762427c8..d2bb70fed8b9 100644
--- a/arch/riscv/kernel/sys_hwprobe.c
+++ b/arch/riscv/kernel/sys_hwprobe.c
@@ -295,6 +295,8 @@ static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
 static void hwprobe_one_pair(struct riscv_hwprobe *pair,
 			     const struct cpumask *cpus)
 {
+	pair->value = 0;
+
 	switch (pair->key) {
 	case RISCV_HWPROBE_KEY_MVENDORID:
 	case RISCV_HWPROBE_KEY_MARCHID:
@@ -329,17 +331,14 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
 		break;
 
 	case RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE:
-		pair->value = 0;
 		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ))
 			pair->value = riscv_cboz_block_size;
 		break;
 	case RISCV_HWPROBE_KEY_ZICBOM_BLOCK_SIZE:
-		pair->value = 0;
 		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOM))
 			pair->value = riscv_cbom_block_size;
 		break;
 	case RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE:
-		pair->value = 0;
 		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOP))
 			pair->value = riscv_cbop_block_size;
 		break;
-- 
2.43.0