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

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