Re: [PATCH v4 13/21] arm64: Allow ID_AA64MMFR1_EL1.VH to be overridden from the command line

Catalin Marinas
2021-01-23T14:07:01Z

On Mon, Jan 18, 2021 at 09:45:25AM +0000, Marc Zyngier wrote:
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index fe0130d6c0ff..80a5f423444e 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -814,6 +814,9 @@ static inline unsigned int get_vmid_bits(u64 mmfr1)
> return 8;
> }
>
> +extern u64 id_aa64mmfr1_val;
> +extern u64 id_aa64mmfr1_mask;
> +
> u32 get_kvm_ipa_limit(void);
> void dump_cpu_features(void);
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 48a011935d8c..5b9343d2e9f0 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -555,6 +555,9 @@ static const struct arm64_ftr_bits ftr_raz[] = {
>
> #define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, NULL, NULL)
>
> +u64 id_aa64mmfr1_val;
> +u64 id_aa64mmfr1_mask;
> +
> static const struct __ftr_reg_entry {
> u32 sys_id;
> struct arm64_ftr_reg *reg;
> @@ -602,7 +605,8 @@ static const struct __ftr_reg_entry {
>
> /* Op1 = 0, CRn = 0, CRm = 7 */
> ARM64_FTR_REG(SYS_ID_AA64MMFR0_EL1, ftr_id_aa64mmfr0),
> - ARM64_FTR_REG(SYS_ID_AA64MMFR1_EL1, ftr_id_aa64mmfr1),
> + ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64MMFR1_EL1, ftr_id_aa64mmfr1,
> + &id_aa64mmfr1_val, &id_aa64mmfr1_mask),
> ARM64_FTR_REG(SYS_ID_AA64MMFR2_EL1, ftr_id_aa64mmfr2),
>
> /* Op1 = 0, CRn = 1, CRm = 2 */
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index 392f93b67103..75d9845f489b 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -10,6 +10,7 @@
> #include <linux/libfdt.h>
>
> #include <asm/cacheflush.h>
> +#include <asm/cpufeature.h>
> #include <asm/setup.h>
>
> struct reg_desc {
> @@ -22,7 +23,18 @@ struct reg_desc {
> } fields[];
> };
>
> +static const struct reg_desc mmfr1 __initdata = {
> + .name = "id_aa64mmfr1",
> + .val = &id_aa64mmfr1_val,
> + .mask = &id_aa64mmfr1_mask,
> + .fields = {
> + { "vh", ID_AA64MMFR1_VHE_SHIFT },
> + {}
> + },
> +};
> +
> static const struct reg_desc * const regs[] __initdata = {
> + &mmfr1,
> };

I'm ok in principle with how all these link together. I wonder however
if we could skip the separate u64 variables and just have a struct
reg_override with val and mask u64 rather than pointers. The
ARM64_FTR_REG_OVERRIDE macro takes a pointer to this new struct
reg_override and can access val/mask directly. Some 'const' may need to
be dropped.

--
Catalin