Re: [PATCH bpf-next v2 0/5] execmem_alloc for BPF programs

[Song Liu <song@kernel.org>]

On Tue, Nov 8, 2022 at 3:44 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
[...]
> >
> > execmem_alloc() manages a set of PMD_SIZE RO+X memory, and allocates these
> > memory to its users. execmem_alloc() is used to free memory allocated by
> > execmem_alloc(). execmem_fill() is used to update memory allocated by
> > execmem_alloc().
> >
> > Memory allocated by execmem_alloc() is RO+X, so this doesnot violate W^X.
> > The caller has to update the content with text_poke like mechanism.
> > Specifically, execmem_fill() is provided to update memory allocated by
> > execmem_alloc(). execmem_fill() also makes sure the update stays in the
> > boundary of one chunk allocated by execmem_alloc(). Please refer to patch
> > 1/5 for more details of
> >
> > Patch 3/5 uses these new APIs in bpf program and bpf dispatcher.
> >
> > Patch 4/5 and 5/5 allows static kernel text (_stext to _etext) to share
> > PMD_SIZE pages with dynamic kernel text on x86_64. This is achieved by
> > allocating PMD_SIZE pages to roundup(_etext, PMD_SIZE), and then use
> > _etext to roundup(_etext, PMD_SIZE) for dynamic kernel text.
>
> Would it be possible to have something more generic than being stuck to
> PMD_SIZE ?
>
> On powerpc 8xx, PMD_SIZE is 4MB and hugepages are 512kB and 8MB.

Currently, __vmalloc_node_range() tries to allocate huge pages when
size_per_node >= PMD_SIZE

How do we handle this in powerpc 8xx? I guess we can use the same logic
here?

Thanks,
Song