[PATCH 5.4.y 01/13] arm64: cpufeature: Force HWCAP to be based on the sysreg visible to user-space

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From: James Morse <james.morse@xxxxxxx>

[ Upstream commit 237405ebef580a7352a52129b2465c117145eafa ]

arm64 advertises hardware features to user-space via HWCAPs, and by
emulating access to the CPUs id registers. The cpufeature code has a
sanitised system-wide view of an id register, and a sanitised user-space
view of an id register, where some features use their 'safe' value
instead of the hardware value.

It is currently possible for a HWCAP to be advertised where the user-space
view of the id register does not show the feature as supported.
Erratum workaround need to remove both the HWCAP, and the feature from
the user-space view of the id register. This involves duplicating the
code, and spreading it over cpufeature.c and cpu_errata.c.

Make the HWCAP code use the user-space view of id registers. This ensures
the values never diverge, and allows erratum workaround to remove HWCAP
by modifying the user-space view of the id register.

Signed-off-by: James Morse <james.morse@xxxxxxx>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Link: https://lore.kernel.org/r/20220909165938.3931307-2-james.morse@xxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
[ Mark: fixup lack of 'width' parameter ]
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
---
 arch/arm64/kernel/cpufeature.c | 36 +++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 396d96224b48b..e4f426c4f2428 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -875,17 +875,39 @@ feature_matches(u64 reg, const struct arm64_cpu_capabilities *entry)
 	return val >= entry->min_field_value;
 }
 
-static bool
-has_cpuid_feature(const struct arm64_cpu_capabilities *entry, int scope)
+static u64
+read_scoped_sysreg(const struct arm64_cpu_capabilities *entry, int scope)
 {
-	u64 val;
-
 	WARN_ON(scope == SCOPE_LOCAL_CPU && preemptible());
 	if (scope == SCOPE_SYSTEM)
-		val = read_sanitised_ftr_reg(entry->sys_reg);
+		return read_sanitised_ftr_reg(entry->sys_reg);
 	else
-		val = __read_sysreg_by_encoding(entry->sys_reg);
+		return __read_sysreg_by_encoding(entry->sys_reg);
+}
 
+static bool
+has_user_cpuid_feature(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	int mask;
+	struct arm64_ftr_reg *regp;
+	u64 val = read_scoped_sysreg(entry, scope);
+
+	regp = get_arm64_ftr_reg(entry->sys_reg);
+	if (!regp)
+		return false;
+
+	mask = cpuid_feature_extract_unsigned_field(regp->user_mask,
+						    entry->field_pos);
+	if (!mask)
+		return false;
+
+	return feature_matches(val, entry);
+}
+
+static bool
+has_cpuid_feature(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	u64 val = read_scoped_sysreg(entry, scope);
 	return feature_matches(val, entry);
 }
 
@@ -1593,7 +1615,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 };
 
 #define HWCAP_CPUID_MATCH(reg, field, s, min_value)				\
-		.matches = has_cpuid_feature,					\
+		.matches = has_user_cpuid_feature,				\
 		.sys_reg = reg,							\
 		.field_pos = field,						\
 		.sign = s,							\
-- 
2.30.2





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