Re: [PATCH bpf-next v5 1/3] btf: allow mmap of vmlinux btf

[Alexei Starovoitov]

On Thu, Jul 17, 2025 at 6:18 AM Lorenz Bauer <lmb@xxxxxxxxxxxxx> wrote:
>
> Hi Breno,
>
> Thanks for reaching out.
>
> On Thu, Jul 17, 2025 at 1:39 PM Breno Leitao <leitao@xxxxxxxxxx> wrote:
>
> > Should __pa_symbol() be used instead of virt_to_phys()?
>
> I'm not really well versed with mm in general. Looking around a bit I
> found some explanation in [1]. Your suggested fix does make sense to
> me based on that.
>
> Let me run the patch against bpf-ci and see what happens.
>
> 1: https://lore.kernel.org/all/90667b2b7f773308318261f96ebefd1a67133c4c.1732464395.git.lukas@xxxxxxxxx/

Thanks for the link.
Key quote: "arm64 maps the kernel in the vmalloc space."
I think the map shouldn't be destroying linearity of kernel rodata.
__pa_symbol() should work for start_BTF, but would be good
to double check with Ard that the rest stays linear.