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

[Song Liu <song@kernel.org>]

On Wed, Dec 7, 2022 at 12:57 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> Song!
>
> On Wed, Dec 07 2022 at 11:26, Song Liu wrote:
> > On Wed, Dec 7, 2022 at 7:36 AM Thomas Gleixner <tglx@linutronix.de> wrote:
> >> > I think we can handle all these with a single module_alloc() and a few
> >> > module_arch_* functions().
> >> struct mod_alloc_type {
> >>         unsigned int    mapto_type;
> >>         unsigned int    flags;
> >>         unsigned int    granularity;
> >>         unsigned int    alignment;
> >>         unsigned long   start[MOD_MAX_ADDR_SPACES];
> >>         unsigned long   end[MOD_MAX_ADDR_SPACES];
> >>         pgprot_t        pgprot;
> >>         void            (*fill)(void *dst, void *src, unsigned int size);
> >>         void            (*invalidate)(void *dst, unsigned int size);
> >> };
> >
> > Yeah, this is a lot better than arch_ functions.
>
> Remember the order of things to worry about: #3 :)
>
> > We probably want two more function pointers here:
> >
> > int (*protect)(unsigned long addr, int numpages);
> > int (*unprotect)(unsigned long addr, int numpages);
> >
> > These two functions will be NULL for archs that support text_poke;
> > while legacy archs use them for set_memory_[ro|x|rw|nx]. Then, I
> > think we can get rid of VM_FLUSH_RESET_PERMS.
>
> Depends. You can implement
>
> fill()
>         memcpy(...);
>         set_memory_ro();
>
> and
>
> invalidate()
>         set_memory_rw();
>         memset();
>
> as global helpers which can be used by the architecture for the init
> struct or used as default for certain types.

Ah, that's right. Legacy archs should always use PAGE_SIZE granularity,
so fill() and invalidate() are sufficient.

>
> > I think I am ready to dive into the code and prepare the first RFC/PATCH.
> > Please let me know if there is anything we should discuss/clarify before that.
>
> I think we covered most of it by now, so sure a POC is probably due, but
> please yell when you find a gap in step #1 - #3 which we did not cover
> yet.

Thanks! Let me see what I can get.

Song