[PATCH v3 09/21] arm64: cpufeature: Add global feature override facility

Marc Zyngier
2021-01-11T13:30:07Z

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 <maz@kernel.org>
---
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 e99eddec0a46..492321054bd5 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