Subject: [PATCH 09/17] arm64: cpufeature: Add global feature override facility

From: Marc Zyngier <[email-masked]>
Date: Mon, 28 Dec 2020 10:49:50 +0000

Add a facility to globally override a feature, no matter what
the HW says. Yes, this is dangerous.

Nothing uses this yet, so we are pretty safe. For now.

Signed-off-by: Marc Zyngier <[email-masked]>
---
 arch/arm64/include/asm/cpufeature.h |  2 ++
 arch/arm64/kernel/cpufeature.c      | 26 +++++++++++++++++++++-----
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9a555809b89c..465d2cb63bfc 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -75,6 +75,8 @@ struct arm64_ftr_reg {
 	u64				sys_val;
 	u64				user_val;
 	const struct arm64_ftr_bits	*ftr_bits;
+	u64				*override_val;
+	u64				*override_mask;
 };
 
 extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 7ffb5f1d8b68..2dbfc0096b0d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -544,13 +544,17 @@ static const struct arm64_ftr_bits ftr_raz[] = {
 	ARM64_FTR_END,
 };
 
-#define ARM64_FTR_REG(id, table) {		\
-	.sys_id = id,				\
-	.reg = 	&(struct arm64_ftr_reg){	\
-		.name = #id,			\
-		.ftr_bits = &((table)[0]),	\
+#define ARM64_FTR_REG_OVERRIDE(id, table, v, m) {		\
+		.sys_id = id,					\
+		.reg = 	&(struct arm64_ftr_reg){		\
+			.name = #id,				\
+			.ftr_bits = &((table)[0]),		\
+			.override_val = v,			\
+			.override_mask = m,			\
 	}}
 
+#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, NULL, NULL)
+
 static const struct __ftr_reg_entry {
 	u32			sys_id;
 	struct arm64_ftr_reg 	*reg;
@@ -786,6 +790,18 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
 
 	val &= valid_mask;
 
+	if (reg->override_mask && reg->override_val) {
+		u64 override = val;
+		override &= ~*reg->override_mask;
+		override |= (*reg->override_val & *reg->override_mask);
+
+		if (val != override)
+			pr_warn("%s: forced from %016llx to %016llx\n",
+				reg->name, val, override);
+
+		val = override;
+	}
+
 	reg->sys_val = val;
 	reg->strict_mask = strict_mask;
 	reg->user_mask = user_mask;
-- 
2.29.2

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