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

Guo Ren
2022-12-06T04:30:11Z

On Mon, Dec 5, 2022 at 11:33 PM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> 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.
Oh, I missed that. Thx.

Reviewed-by: Guo Ren <guoren@kernel.org>

>
> 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

--
Best Regards
Guo Ren