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arm64: cpufeature: Add global feature override facility

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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>
Link: https://lore.kernel.org/r/20210208095732.3267263-11-maz@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Marc Zyngier 2021-02-08 09:57:19 +00:00 committed by Will Deacon
parent d077cb3cb9
commit 8f266a5d87
2 changed files with 45 additions and 6 deletions
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6
arch/arm64/include/asm/cpufeature.h
View File

@ -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;
};

45
arch/arm64/kernel/cpufeature.c
View File

@ -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);