Re: [PATCH v2 09/13] riscv: switch to relative alternative entries

Guo Ren
2022-12-05T00:52:00Z

On Mon, Dec 5, 2022 at 1:57 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> Instead of using absolute addresses for both the old instrucions and
> the alternative instructions, use offsets relative to the alt_entry
> values. So we can not only cut the size of the alternative entry, but
> also meet 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 | 13 ++++++-------
> 5 files changed, 33 insertions(+), 27 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,
(void *)&alt->alt_offset + alt->alt_offset. ??!!

> + alt->alt_len);
> cpu_apply_errata |= tmp;
> }
> }
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 21546937db39..2a6e335b5a32 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -68,6 +68,7 @@ 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, *updptr;
>
> for (alt = begin; alt < end; alt++) {
> if (alt->vendor_id != THEAD_VENDOR_ID)
> @@ -77,12 +78,16 @@ 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;
> + updptr = (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(updptr),
> + alt->alt_len);
> else
> - patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
> + patch_text_nosync(oldptr, updptr, alt->alt_len);
> }
> }
>
> diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
> index ec2f3f1b836f..dd40727bc859 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
> .endm
>
> .macro ALT_NEW_CONTENT vendor_id, errata_id, enable = 1, new_c : vararg
> @@ -75,11 +75,11 @@
> #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 33eae9541684..3baf32e05b46 100644
> --- a/arch/riscv/include/asm/alternative.h
> +++ b/arch/riscv/include/asm/alternative.h
> @@ -33,12 +33,12 @@ void riscv_alternative_fix_jal(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 to original instruciton or data */
> + s32 alt_offset; /* offset 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 6244be5cd94a..adeac90b1d8e 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -257,6 +257,7 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
> unsigned int stage)
> {
> struct alt_entry *alt;
> + void *oldptr, *updptr;
>
> if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> return;
> @@ -270,17 +271,15 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
> continue;
> }
>
> + oldptr = (void *)&alt->old_offset + alt->old_offset;
> + updptr = (void *)&alt->alt_offset + alt->alt_offset;
> if (!__riscv_isa_extension_available(NULL, alt->errata_id))
> continue;
>
> /* do the basic patching */
> - patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
> - riscv_alternative_fix_auipc_jalr(alt->old_ptr,
> - alt->alt_len,
> - alt->old_ptr - alt->alt_ptr);
> - riscv_alternative_fix_jal(alt->old_ptr,
> - alt->alt_len,
> - alt->old_ptr - alt->alt_ptr);
> + patch_text_nosync(oldptr, updptr, alt->alt_len);
> + riscv_alternative_fix_auipc_jalr(oldptr, alt->alt_len, oldptr - updptr);
> + riscv_alternative_fix_jal(oldptr, alt->alt_len, oldptr - updptr);
> }
> }
> #endif
> --
> 2.37.2
>

--
Best Regards
Guo Ren