[PATCH v7 10/23] arm64: cpufeature: Add global feature override facility

Marc Zyngier
2021-02-08T10:23:39Z

Add a facility to globally override a feature, no matter what
the HW says. Yes, this sounds dangerous, but we do respect the
"safe" value for a given feature. This doesn't mean the user
doesn't need to know what they are doing.

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

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: David Brazdil <dbrazdil@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/cpufeature.h | 6 ++++
arch/arm64/kernel/cpufeature.c | 45 +++++++++++++++++++++++++----
2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9a555809b89c..b1f53147e2b2 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -63,6 +63,11 @@ struct arm64_ftr_bits {
s64 safe_val; /* safe value for FTR_EXACT features */
};

+struct arm64_ftr_override {
+ u64 val;
+ u64 mask;
+};
+
/*
* @arm64_ftr_reg - Feature register
* @strict_mask Bits which should match across all CPUs for sanity.
@@ -74,6 +79,7 @@ struct arm64_ftr_reg {
u64 user_mask;
u64 sys_val;
u64 user_val;
+ struct arm64_ftr_override *override;
const struct arm64_ftr_bits *ftr_bits;
};

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index e99eddec0a46..a4e5c619a516 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -352,9 +352,12 @@ static const struct arm64_ftr_bits ftr_ctr[] = {
ARM64_FTR_END,
};

+static struct arm64_ftr_override __ro_after_init no_override = { };
+
struct arm64_ftr_reg arm64_ftr_reg_ctrel0 = {
.name = "SYS_CTR_EL0",
- .ftr_bits = ftr_ctr
+ .ftr_bits = ftr_ctr,
+ .override = &no_override,
};

static const struct arm64_ftr_bits ftr_id_mmfr0[] = {
@@ -544,13 +547,16 @@ 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, ovr) { \
+ .sys_id = id, \
+ .reg = &(struct arm64_ftr_reg){ \
+ .name = #id, \
+ .override = (ovr), \
+ .ftr_bits = &((table)[0]), \
}}

+#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, &no_override)
+
static const struct __ftr_reg_entry {
u32 sys_id;
struct arm64_ftr_reg *reg;
@@ -770,6 +776,33 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) {
u64 ftr_mask = arm64_ftr_mask(ftrp);
s64 ftr_new = arm64_ftr_value(ftrp, new);
+ s64 ftr_ovr = arm64_ftr_value(ftrp, reg->override->val);
+
+ if ((ftr_mask & reg->override->mask) == ftr_mask) {
+ s64 tmp = arm64_ftr_safe_value(ftrp, ftr_ovr, ftr_new);
+ char *str = NULL;
+
+ if (ftr_ovr != tmp) {
+ /* Unsafe, remove the override */
+ reg->override->mask &= ~ftr_mask;
+ reg->override->val &= ~ftr_mask;
+ tmp = ftr_ovr;
+ str = "ignoring override";
+ } else if (ftr_new != tmp) {
+ /* Override was valid */
+ ftr_new = tmp;
+ str = "forced";
+ } else if (ftr_ovr == tmp) {
+ /* Override was the safe value */
+ str = "already set";
+ }
+
+ if (str)
+ pr_warn("%s[%d:%d]: %s to %llx\n",
+ reg->name,
+ ftrp->shift + ftrp->width - 1,
+ ftrp->shift, str, tmp);
+ }

val = arm64_ftr_set_value(ftrp, val, ftr_new);

--
2.29.2