Re: [PATCH v2 10/13] riscv: alternative: patch alternatives in the vDSO

Jisheng Zhang
2022-12-05T15:34:21Z

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