linux-kernel - Re: [PATCH 2/4] powerpc/mm: Handle VDSO unmapping via close() rather than arch

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Message-ID: <CALmYWFsCrMxkA1v58fJxtyGR15ZGxmSP8x7QC=oeKwzcwGL76A@mail.gmail.com>
Date: Wed, 7 Aug 2024 08:43:57 -0700
From: Jeff Xu <jeffxu@...gle.com>
To: Michael Ellerman <mpe@...erman.id.au>
Cc: linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org, 
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org, 
	christophe.leroy@...roup.eu, jeffxu@...omium.org, Liam.Howlett@...cle.com, 
	linux-kernel@...r.kernel.org, npiggin@...il.com, oliver.sang@...el.com, 
	pedro.falcato@...il.com, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 2/4] powerpc/mm: Handle VDSO unmapping via close() rather
 than arch_unmap()

On Wed, Aug 7, 2024 at 5:41 AM Michael Ellerman <mpe@...erman.id.au> wrote:
>
> Add a close() callback to the VDSO special mapping to handle unmapping
> of the VDSO. That will make it possible to remove the arch_unmap() hook
> entirely in a subsequent patch.
>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> ---
>  arch/powerpc/include/asm/mmu_context.h |  4 ----
>  arch/powerpc/kernel/vdso.c             | 17 +++++++++++++++++
>  2 files changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
> index 37bffa0f7918..9b8c1555744e 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -263,10 +263,6 @@ extern void arch_exit_mmap(struct mm_struct *mm);
>  static inline void arch_unmap(struct mm_struct *mm,
>                               unsigned long start, unsigned long end)
>  {
> -       unsigned long vdso_base = (unsigned long)mm->context.vdso;
> -
> -       if (start <= vdso_base && vdso_base < end)
> -               mm->context.vdso = NULL;
>  }
>
>  #ifdef CONFIG_PPC_MEM_KEYS
> diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
> index 7a2ff9010f17..220a76cae7c1 100644
> --- a/arch/powerpc/kernel/vdso.c
> +++ b/arch/powerpc/kernel/vdso.c
> @@ -81,6 +81,21 @@ static int vdso64_mremap(const struct vm_special_mapping *sm, struct vm_area_str
>         return vdso_mremap(sm, new_vma, &vdso64_end - &vdso64_start);
>  }
>
> +static void vdso_close(const struct vm_special_mapping *sm, struct vm_area_struct *vma)
> +{
> +       struct mm_struct *mm = vma->vm_mm;
> +
> +       /*
> +        * close() is called for munmap() but also for mremap(). In the mremap()
> +        * case the vdso pointer has already been updated by the mremap() hook
> +        * above, so it must not be set to NULL here.
> +        */
> +       if (vma->vm_start != (unsigned long)mm->context.vdso)
> +               return;
> +
> +       mm->context.vdso = NULL;
> +}
> +
>  static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
>                              struct vm_area_struct *vma, struct vm_fault *vmf);
>
> @@ -92,11 +107,13 @@ static struct vm_special_mapping vvar_spec __ro_after_init = {
>  static struct vm_special_mapping vdso32_spec __ro_after_init = {
>         .name = "[vdso]",
>         .mremap = vdso32_mremap,
> +       .close = vdso_close,
IIUC, only CHECKPOINT_RESTORE requires this, and
CHECKPOINT_RESTORE is in init/Kconfig, with default N

Can we add #ifdef CONFIG_CHECKPOINT_RESTORE here ?

Thanks
Best regards,
-Jeff

>  };
>
>  static struct vm_special_mapping vdso64_spec __ro_after_init = {
>         .name = "[vdso]",
>         .mremap = vdso64_mremap,
> +       .close = vdso_close,
>  };
>
>  #ifdef CONFIG_TIME_NS
> --
> 2.45.2
>