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

[Song Liu <song@kernel.org>]

On Wed, Dec 7, 2022 at 8:54 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 07/12/2022 à 16:36, Thomas Gleixner a écrit :
> >
> > The "use free space in existing mappings" mechanism is not required to
> > be PMD_SIZE based, right?
> >
> > Large page size, strict separation:
> >
> > struct mod_alloc_type_params {
> >       [MOD_ALLOC_TYPE_TEXT] = {
> >               .mapto_type     = MOD_ALLOC_TYPE_TEXT,
> >                  .flags               = FLAG_SHARED_PMD | FLAG_SECOND_ADDRESS_SPACE,
> >                  .granularity = PMD_SIZE,
> >                  .alignment   = MOD_ARCH_ALIGNMENT,
> >                  .start[0]    = MODULES_VADDR,
> >                  .end[0]              = MODULES_END,
> >                  .start[1]    = MODULES_VADDR_2ND,
> >                  .end[1]              = MODULES_END_2ND,
> >                  .pgprot              = PAGE_KERNEL_EXEC,
> >                  .fill                = text_poke,
> >                  .invalidate  = text_poke_invalidate,
> >       },
>
> Don't restrict implementation to PMD_SIZE only.
>
> On powerpc 8xx:
> - PMD_SIZE is 4 Mbytes
> - Large pages are 512 kbytes and 8 Mbytes.
>
> It even has large pages of size 16 kbytes when build for 4k normal page
> size.

IIUC, these customizations would fit nicely with this design. I will see how
much I can prototype with powerpc without the actual hardwares.

Thanks,
Song