Commit 8f266a5d authored by Marc Zyngier's avatar Marc Zyngier Committed by Will Deacon
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arm64: cpufeature: Add global feature override facility 



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: default avatarMarc Zyngier <maz@kernel.org>
Reviewed-by: default avatarSuzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: default avatarDavid Brazdil <dbrazdil@google.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210208095732.3267263-11-maz@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent d077cb3c

arch/arm64/include/asm/cpufeature.h

+6 −0
Original line number Diff line number Diff line
@@ -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;

};

arch/arm64/kernel/cpufeature.c

+39 −6
Original line number Diff line number Diff line
@@ -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) {		\

#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);