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

Guo Ren
2022-12-05T01:56:56Z

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.

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