Re: [PATCH v2 bpf] lib/buildid: handle memfd_secret() files in build_id_parse()

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Oct 17, 2024 at 10:54 AM Heiko Carstens <hca@linux.ibm.com> wrote:
>
> On Thu, Oct 17, 2024 at 10:35:27AM -0700, Andrii Nakryiko wrote:
> > On Thu, Oct 17, 2024 at 9:35 AM Shakeel Butt <shakeel.butt@linux.dev> wrote:
> > > On Thu, Oct 17, 2024 at 11:18:34AM GMT, David Hildenbrand wrote:
> > > > As replied elsewhere, can't we take a look at the mapping?
> > > >
> > > > We do the same thing in gup_fast_folio_allowed() where we check
> > > > secretmem_mapping().
> > >
> > > Responded on the v1 but I think we can go with v1 of this work as
> > > whoever will be working on unmapping folios from direct map will need to
> > > fix gup_fast_folio_allowed(), they can fix this code as well. Also it
> > > seems like some arch don't have kernel_page_present() and builds are
> > > failing.
> > >
> >
> > Yeah, we are lucky that BPF CI tested s390x and caught this issue.
> >
> > > Andrii, let's move forward with the v1 patch.
> >
> > Let me post v3 based on v1 (checking for secretmem_mapping()), but
> > I'll change return code to -EFAULT, so in the future this can be
> > rolled into generic error handling code path with no change in error
> > code.
>
> Ok, I've seen that you don't need kernel_page_present() anymore, just
> after I implemented it for s390. I guess I'll send the patch below
> (with a different commit message) upstream anyway, just in case
> somebody else comes up with a similar use case.

Please do send a patch, yes. It's good to have complete implementation
of this API regardless. We can then switch to either
kernel_page_present() or an alternative approach mentioned in [0] by
David Hildenbrand, in the next release cycle, for instance. Thanks.

  [0] https://lore.kernel.org/all/c87a4ba0-b9c4-4044-b0c3-c1112601494f@redhat.com/

>
> From b625edc35de64293b728b030c62f7aaa65c8627e Mon Sep 17 00:00:00 2001
> From: Heiko Carstens <hca@linux.ibm.com>
> Date: Thu, 17 Oct 2024 19:41:07 +0200
> Subject: [PATCH] s390/pageattr: Implement missing kernel_page_present()
>
> kernel_page_present() was intentionally not implemented when adding
> ARCH_HAS_SET_DIRECT_MAP support, since it was only used for suspend/resume
> which is not supported anymore on s390.
>
> However a new bpf use case now leads to a compile error specific to
> s390. Implement kernel_page_present() to fix this.
>
> Reported-by: Daniel Borkmann <daniel@iogearbox.net>
> Closes: https://lore.kernel.org/all/045de961-ac69-40cc-b141-ab70ec9377ec@iogearbox.net
> Fixes: 0490d6d7ba0a ("s390/mm: enable ARCH_HAS_SET_DIRECT_MAP")
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
>  arch/s390/include/asm/set_memory.h |  1 +
>  arch/s390/mm/pageattr.c            | 15 +++++++++++++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/arch/s390/include/asm/set_memory.h b/arch/s390/include/asm/set_memory.h
> index 06fbabe2f66c..cb4cc0f59012 100644
> --- a/arch/s390/include/asm/set_memory.h
> +++ b/arch/s390/include/asm/set_memory.h
> @@ -62,5 +62,6 @@ __SET_MEMORY_FUNC(set_memory_4k, SET_MEMORY_4K)
>
>  int set_direct_map_invalid_noflush(struct page *page);
>  int set_direct_map_default_noflush(struct page *page);
> +bool kernel_page_present(struct page *page);
>
>  #endif
> diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
> index 5f805ad42d4c..aec9eb16b6f7 100644
> --- a/arch/s390/mm/pageattr.c
> +++ b/arch/s390/mm/pageattr.c
> @@ -406,6 +406,21 @@ int set_direct_map_default_noflush(struct page *page)
>         return __set_memory((unsigned long)page_to_virt(page), 1, SET_MEMORY_DEF);
>  }
>
> +bool kernel_page_present(struct page *page)
> +{
> +       unsigned long addr;
> +       unsigned int cc;
> +
> +       addr = (unsigned long)page_address(page);
> +       asm volatile(
> +               "       lra     %[addr],0(%[addr])\n"
> +               "       ipm     %[cc]\n"
> +               : [cc] "=d" (cc), [addr] "+a" (addr)
> +               :
> +               : "cc");
> +       return (cc >> 28) == 0;
> +}
> +
>  #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KFENCE)
>
>  static void ipte_range(pte_t *pte, unsigned long address, int nr)
> --
> 2.45.2
>