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    SubjectRe: [PATCH v2 10/13] riscv: alternative: patch alternatives in the vDSO
    On Mon, Dec 05, 2022 at 09:56:37AM +0800, Guo Ren wrote:
    > Are there any patches that depend on it? Any existing utilization? My
    > first idea is to let __vdso_flush_icache use it, the standard
    > implementation is so heavy for user space JIT scenario, maybe vendors
    > could give a custom one.

    Hi Guo,

    the 11th patch of swtiching cpu_relax() to riscv_has_extension_likely()
    depends on this patch, the gettimeofday implementation calls cpu_relax()
    which may use ZIHINTPAUSE extension, so we need to patch vDSO.

    Thanks

    >
    > On Mon, Dec 5, 2022 at 1:57 AM Jisheng Zhang <jszhang@kernel.org> wrote:
    > >
    > > Make it possible to use alternatives in the vDSO, so that better
    > > implementations can be used if possible.
    > >
    > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
    > > ---
    > > arch/riscv/include/asm/vdso.h | 4 ++++
    > > arch/riscv/kernel/alternative.c | 25 +++++++++++++++++++++++++
    > > arch/riscv/kernel/vdso.c | 5 -----
    > > arch/riscv/kernel/vdso/vdso.lds.S | 7 +++++++
    > > 4 files changed, 36 insertions(+), 5 deletions(-)
    > >
    > > diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
    > > index af981426fe0f..b6ff7473fb8a 100644
    > > --- a/arch/riscv/include/asm/vdso.h
    > > +++ b/arch/riscv/include/asm/vdso.h
    > > @@ -28,8 +28,12 @@
    > > #define COMPAT_VDSO_SYMBOL(base, name) \
    > > (void __user *)((unsigned long)(base) + compat__vdso_##name##_offset)
    > >
    > > +extern char compat_vdso_start[], compat_vdso_end[];
    > > +
    > > #endif /* CONFIG_COMPAT */
    > >
    > > +extern char vdso_start[], vdso_end[];
    > > +
    > > #endif /* !__ASSEMBLY__ */
    > >
    > > #endif /* CONFIG_MMU */
    > > diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
    > > index 9d88375624b5..eaf7ddaba54c 100644
    > > --- a/arch/riscv/kernel/alternative.c
    > > +++ b/arch/riscv/kernel/alternative.c
    > > @@ -11,7 +11,9 @@
    > > #include <linux/cpu.h>
    > > #include <linux/uaccess.h>
    > > #include <asm/alternative.h>
    > > +#include <asm/module.h>
    > > #include <asm/sections.h>
    > > +#include <asm/vdso.h>
    > > #include <asm/vendorid_list.h>
    > > #include <asm/sbi.h>
    > > #include <asm/csr.h>
    > > @@ -187,6 +189,27 @@ static void __init_or_module _apply_alternatives(struct alt_entry *begin,
    > > stage);
    > > }
    > >
    > > +static void __init apply_vdso_alternatives(void)
    > > +{
    > > + const struct elf64_hdr *hdr;
    > > + const struct elf64_shdr *shdr;
    > > + const struct elf64_shdr *alt;
    > > + struct alt_entry *begin, *end;
    > > +
    > > + hdr = (struct elf64_hdr *)vdso_start;
    > > + shdr = (void *)hdr + hdr->e_shoff;
    > > + alt = find_section(hdr, shdr, ".alternative");
    > > + if (!alt)
    > > + return;
    > > +
    > > + begin = (void *)hdr + alt->sh_offset,
    > > + end = (void *)hdr + alt->sh_offset + alt->sh_size,
    > > +
    > > + _apply_alternatives((struct alt_entry *)begin,
    > > + (struct alt_entry *)end,
    > > + RISCV_ALTERNATIVES_BOOT);
    > > +}
    > > +
    > > void __init apply_boot_alternatives(void)
    > > {
    > > /* If called on non-boot cpu things could go wrong */
    > > @@ -195,6 +218,8 @@ void __init apply_boot_alternatives(void)
    > > _apply_alternatives((struct alt_entry *)__alt_start,
    > > (struct alt_entry *)__alt_end,
    > > RISCV_ALTERNATIVES_BOOT);
    > > +
    > > + apply_vdso_alternatives();
    > > }
    > >
    > > /*
    > > diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
    > > index 123d05255fcf..1f47bc6566cf 100644
    > > --- a/arch/riscv/kernel/vdso.c
    > > +++ b/arch/riscv/kernel/vdso.c
    > > @@ -22,11 +22,6 @@ struct vdso_data {
    > > };
    > > #endif
    > >
    > > -extern char vdso_start[], vdso_end[];
    > > -#ifdef CONFIG_COMPAT
    > > -extern char compat_vdso_start[], compat_vdso_end[];
    > > -#endif
    > > -
    > > enum vvar_pages {
    > > VVAR_DATA_PAGE_OFFSET,
    > > VVAR_TIMENS_PAGE_OFFSET,
    > > diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
    > > index 150b1a572e61..4a0606633290 100644
    > > --- a/arch/riscv/kernel/vdso/vdso.lds.S
    > > +++ b/arch/riscv/kernel/vdso/vdso.lds.S
    > > @@ -40,6 +40,13 @@ SECTIONS
    > > . = 0x800;
    > > .text : { *(.text .text.*) } :text
    > >
    > > + . = ALIGN(4);
    > > + .alternative : {
    > > + __alt_start = .;
    > > + *(.alternative)
    > > + __alt_end = .;
    > > + }
    > > +
    > > .data : {
    > > *(.got.plt) *(.got)
    > > *(.data .data.* .gnu.linkonce.d.*)
    > > --
    > > 2.37.2
    > >
    >
    >
    > --
    > Best Regards
    > Guo Ren

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