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

From: Guo Ren
Date: Mon Dec 05 2022 - 23:35:12 EST

On Mon, Dec 5, 2022 at 11:28 PM Jisheng Zhang <jszhang@xxxxxxxxxx> wrote:
>
> On Mon, Dec 05, 2022 at 08:51:41AM +0800, Guo Ren wrote:
> > On Mon, Dec 5, 2022 at 1:57 AM Jisheng Zhang <jszhang@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > > 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. ??!!
>
> Hi Guo,
>
> what's the problem? I can't catch your meaning, could you please proide
> more details?
Can you explain why:

alt->old_ptr = (void *)&alt->old_offset + alt->old_offset

| offset | <- &offset
| ... |
| value | <- ptr = &offset + offset

I don't make sense of the above.

>
> Thanks
>
> >
> > > + 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



--
Best Regards
Guo Ren