Re: [PATCHv7 08/14] x86/mm: Reserve unaccepted memory bitmap

Kirill A. Shutemov
2022-11-30T01:28:45Z

On Tue, Jul 26, 2022 at 11:07:14AM +0200, Borislav Petkov wrote:
> On Tue, Jun 14, 2022 at 03:02:25PM +0300, Kirill A. Shutemov wrote:
> > diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> > index f267205f2d5a..22d1fe48dcba 100644
> > --- a/arch/x86/kernel/e820.c
> > +++ b/arch/x86/kernel/e820.c
> > @@ -1316,6 +1316,16 @@ void __init e820__memblock_setup(void)
> > int i;
> > u64 end;
> >
> > + /* Mark unaccepted memory bitmap reserved */
> > + if (boot_params.unaccepted_memory) {
> > + unsigned long size;
> > +
> > + /* One bit per 2MB */
> > + size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE,
> > + PMD_SIZE * BITS_PER_BYTE);
> > + memblock_reserve(boot_params.unaccepted_memory, size);
> > + }
> > +
>
> Hmm, I don't like how this is dropped right in the middle of a unrelated
> function.
>
> You're adding arch/x86/mm/unaccepted_memory.c later. Why don't you put
> that chunk in a function there which is called by early_reserve_memory()
> which does exactly what you want - reserve memory early, before memblock
> allocations?

early_reserve_memory() specifically called before e820__memory_setup()
(see comment in setup_arch()), so we don't have e820_table finalized and
we need it to get correct RAM size from e820__end_of_ram_pfn().

I guess we can hide the chunk in a function in unaccepted_memory.c and
call it from here, but it would require #ifdeffery in a header file as the
.c is only compiled for CONFIG_UNACCEPTED_MEMORY=y.

Looks like an overkill to me, no?

--
Kiryl Shutsemau / Kirill A. Shutemov