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arm64: errata: match the target implementation CPU's own MIDR

PATCH Applied David Carlier 2 participants 2 messages Sep 6 – Sep 18

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Stable branch arm64
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David Carlier

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#0 lore raw

PATCH 1/1 arm64: errata: match the target implementation CPU's own MIDR

__is_affected_midr_range() is handed the MIDR and REVIDR of one target implementation CPU, but tests the erratum's range with is_midr_in_range(), which re-scans all of target_impl_cpus[] and ignores the @midr argument. The range test is thus constant across the per-CPU loop in is_affected_midr_range() and only answers "is any target CPU in range".

Since just the fixed_revs REVIDR check uses the iteration's own registers, an out-of-range target CPU can decide whether a MIDR_FIXED() exemption applies. A VM then enables a workaround whose only in-range CPU is fixed silicon, e.g. erratum 2658417 on a Cortex-A510 r1p1 with REVIDR_EL1[25] set.

Factor the range test into __is_midr_in_range(), which takes an explicit MIDR, and use it in __is_affected_midr_range().

Fixes 86edf6bdcf05 ("smccc/kvm_guest: Enable errata based on implementation CPUs")
Cc [email protected]
Assisted-by Claude:claude-opus-5
Signed-off-by David Carlier <[email protected]>
---
 arch/arm64/kernel/cpu_errata.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)
arch/arm64/kernel/cpu_errata.c +9 -6
index b33dccfafaf8..8ec47d89b45b 100644
@@ -28,18 +28,21 @@ bool cpu_errata_set_target_impl(u64 num, void *impl_cpus)
 	return true;
 }
 
+static inline bool __is_midr_in_range(u32 midr, struct midr_range const *range)
+{
+	return midr_is_cpu_model_range(midr, range->model,
+				       range->rv_min, range->rv_max);
+}
+
 static inline bool is_midr_in_range(struct midr_range const *range)
 {
 	int i;
 
 	if (!target_impl_cpu_num)
-		return midr_is_cpu_model_range(read_cpuid_id(), range->model,
-					       range->rv_min, range->rv_max);
+		return __is_midr_in_range(read_cpuid_id(), range);
 
 	for (i = 0; i < target_impl_cpu_num; i++) {
-		if (midr_is_cpu_model_range(target_impl_cpus[i].midr,
-					    range->model,
-					    range->rv_min, range->rv_max))
+		if (__is_midr_in_range(target_impl_cpus[i].midr, range))
 			return true;
 	}
 	return false;

@@ -59,7 +62,7 @@ __is_affected_midr_range(const struct arm64_cpu_capabilities *entry,
 			 u32 midr, u32 revidr)
 {
 	const struct arm64_midr_revidr *fix;
-	if (!is_midr_in_range(&entry->midr_range))
+	if (!__is_midr_in_range(midr, &entry->midr_range))
 		return false;
 
 	midr &= MIDR_REVISION_MASK | MIDR_VARIANT_MASK;
Signature · 1 line
2.55.0
maintainer Applied
#1 lore raw
Quoted 6 lines · David Carlier

__is_affected_midr_range() is handed the MIDR and REVIDR of one target implementation CPU, but tests the erratum's range with is_midr_in_range(), which re-scans all of target_impl_cpus[] and ignores the @midr argument. The range test is thus constant across the per-CPU loop in is_affected_midr_range() and only answers "is any target CPU in range".

Quoted 7 lines

Since just the fixed_revs REVIDR check uses the iteration's own registers, an out-of-range target CPU can decide whether a MIDR_FIXED() exemption applies. A VM then enables a workaround whose only in-range CPU is fixed silicon, e.g. erratum 2658417 on a Cortex-A510 r1p1 with REVIDR_EL1[25] set.

[...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: errata: match the target implementation CPU's own MIDR

      https://git.kernel.org/arm64/c/b7403afb7a5f

Cheers,

Signature · 5 lines
Will

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