Re: [PATCH v4 09/21] arm64: cpufeature: Add global feature override facility

Catalin Marinas
2021-01-22T19:35:57Z

On Mon, Jan 18, 2021 at 09:45:21AM +0000, Marc Zyngier wrote:
> 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..aaa075c6f029 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;
> @@ -760,6 +764,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
> u64 strict_mask = ~0x0ULL;
> u64 user_mask = 0;
> u64 valid_mask = 0;
> + u64 override_val = 0, override_mask = 0;
>
> const struct arm64_ftr_bits *ftrp;
> struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg);
> @@ -767,9 +772,38 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
> if (!reg)
> return;
>
> + if (reg->override_mask && reg->override_val) {
> + override_mask = *reg->override_mask;
> + override_val = *reg->override_val;
> + }
> +
> 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, override_val);
> +
> + if ((ftr_mask & 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;

Do we need such clearing here? I don't think that's ever called again
for this feature/reg.

> + tmp = ftr_ovr;
> + str = "ignoring override";
> + } else if (ftr_new != tmp) {
> + /* Override was valid */
> + ftr_new = tmp;
> + str = "forced";
> + }
> +
> + 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);

I wonder whether we could call, after init_cpu_ftr_reg(), a new function
similar to update_cpu_ftr_reg() that takes a mask and value and leave
init_cpu_ftr_reg() unchanged. The only advantage would be if we can get
rid of the reg->override* fields. Anyway, I need to read the rest of the
series to see whether it's possible. Otherwise this patch looks fine.

--
Catalin