Re: [PATCH v3 09/13] riscv: switch to relative alternative entries

Andrew Jones
2023-01-11T18:12:13Z

On Thu, Jan 12, 2023 at 01:10:23AM +0800, Jisheng Zhang wrote:
> Instead of using absolute addresses for both the old instrucions and
> the alternative instructions, use offsets relative to the alt_entry
> values. So this not only cuts the size of the alternative entry, but
> also meets the prerequisite for patching alternatives in the vDSO,
> since absolute alternative entries are subject to dynamic relocation,
> which is incompatible with the vDSO building.
>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
> arch/riscv/errata/sifive/errata.c | 4 +++-
> arch/riscv/errata/thead/errata.c | 11 ++++++++---
> arch/riscv/include/asm/alternative-macros.h | 20 ++++++++++----------
> arch/riscv/include/asm/alternative.h | 12 ++++++------
> arch/riscv/kernel/cpufeature.c | 8 +++++---
> 5 files changed, 32 insertions(+), 23 deletions(-)
>
> diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
> index 1031038423e7..0e537cdfd324 100644
> --- a/arch/riscv/errata/sifive/errata.c
> +++ b/arch/riscv/errata/sifive/errata.c
> @@ -107,7 +107,9 @@ void __init_or_module sifive_errata_patch_func(struct alt_entry *begin,
>
> tmp = (1U << alt->errata_id);
> if (cpu_req_errata & tmp) {
> - patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
> + patch_text_nosync((void *)&alt->old_offset + alt->old_offset,
> + (void *)&alt->alt_offset + alt->alt_offset,

I was hoping to see Conor's macro suggestion show up in this version.

> + alt->alt_len);
> cpu_apply_errata |= tmp;
> }
> }
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index fac5742d1c1e..d56d76a529b5 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -87,6 +87,7 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
> struct alt_entry *alt;
> u32 cpu_req_errata = thead_errata_probe(stage, archid, impid);
> u32 tmp;
> + void *oldptr, *altptr;
>
> for (alt = begin; alt < end; alt++) {
> if (alt->vendor_id != THEAD_VENDOR_ID)
> @@ -96,12 +97,16 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
>
> tmp = (1U << alt->errata_id);
> if (cpu_req_errata & tmp) {
> + oldptr = (void *)&alt->old_offset + alt->old_offset;
> + altptr = (void *)&alt->alt_offset + alt->alt_offset;
> +
> /* On vm-alternatives, the mmu isn't running yet */
> if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> - memcpy((void *)__pa_symbol(alt->old_ptr),
> - (void *)__pa_symbol(alt->alt_ptr), alt->alt_len);
> + memcpy((void *)__pa_symbol(oldptr),
> + (void *)__pa_symbol(altptr),
> + alt->alt_len);
> else
> - patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
> + patch_text_nosync(oldptr, altptr, alt->alt_len);
> }
> }
>
> diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
> index 7226e2462584..3c3ca65e521b 100644
> --- a/arch/riscv/include/asm/alternative-macros.h
> +++ b/arch/riscv/include/asm/alternative-macros.h
> @@ -7,11 +7,11 @@
> #ifdef __ASSEMBLY__
>
> .macro ALT_ENTRY oldptr newptr vendor_id errata_id new_len
> - RISCV_PTR \oldptr
> - RISCV_PTR \newptr
> - REG_ASM \vendor_id
> - REG_ASM \new_len
> - .word \errata_id
> + .long \oldptr - .
> + .long \newptr - .
> + .short \vendor_id
> + .short \new_len
> + .long \errata_id

nit: I like .2byte and .4byte since I always have to double check how many
bytes .long is.

> .endm
>
> .macro ALT_NEW_CONTENT vendor_id, errata_id, enable = 1, new_c : vararg
> @@ -59,11 +59,11 @@
> #include <linux/stringify.h>
>
> #define ALT_ENTRY(oldptr, newptr, vendor_id, errata_id, newlen) \
> - RISCV_PTR " " oldptr "\n" \
> - RISCV_PTR " " newptr "\n" \
> - REG_ASM " " vendor_id "\n" \
> - REG_ASM " " newlen "\n" \
> - ".word " errata_id "\n"
> + ".long ((" oldptr ") - .) \n" \
> + ".long ((" newptr ") - .) \n" \
> + ".short " vendor_id "\n" \
> + ".short " newlen "\n" \
> + ".long " errata_id "\n"
>
> #define ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c) \
> ".if " __stringify(enable) " == 1\n" \
> diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
> index 1bd4027d34ca..b6050a235f50 100644
> --- a/arch/riscv/include/asm/alternative.h
> +++ b/arch/riscv/include/asm/alternative.h
> @@ -31,12 +31,12 @@ void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
> int patch_offset);
>
> struct alt_entry {
> - void *old_ptr; /* address of original instruciton or data */
> - void *alt_ptr; /* address of replacement instruction or data */
> - unsigned long vendor_id; /* cpu vendor id */
> - unsigned long alt_len; /* The replacement size */
> - unsigned int errata_id; /* The errata id */
> -} __packed;
> + s32 old_offset; /* offset relative to original instruciton or data */
^
instruction

(The typo was already there, but, IMO, we can fix something like that
while touching it.)

> + s32 alt_offset; /* offset relative to replacement instruction or data */
> + u16 vendor_id; /* cpu vendor id */
> + u16 alt_len; /* The replacement size */
> + u32 errata_id; /* The errata id */
> +};
>
> struct errata_checkfunc_id {
> unsigned long vendor_id;
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 6db8b31d9149..c394cde2560b 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -280,6 +280,7 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
> unsigned int stage)
> {
> struct alt_entry *alt;
> + void *oldptr, *altptr;
>
> if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> return;
> @@ -293,12 +294,13 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
> continue;
> }
>
> + oldptr = (void *)&alt->old_offset + alt->old_offset;
> + altptr = (void *)&alt->alt_offset + alt->alt_offset;
> if (!__riscv_isa_extension_available(NULL, alt->errata_id))
> continue;
>
> - patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
> - riscv_alternative_fix_offsets(alt->old_ptr, alt->alt_len,
> - alt->old_ptr - alt->alt_ptr);
> + patch_text_nosync(oldptr, altptr, alt->alt_len);
> + riscv_alternative_fix_offsets(oldptr, alt->alt_len, oldptr - altptr);
> }
> }
> #endif
> --
> 2.38.1

Besides preferring a macro and the nits, LGTM

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Thanks,
drew