linux-kernel - Re: [PATCH] mm: check pfn_valid first in zero_resv

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Date:   Fri, 1 Dec 2017 10:42:15 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Dave Young <dyoung@...hat.com>
Cc:     linux-kernel@...r.kernel.org, pasha.tatashin@...cle.com,
        linux-mm@...ck.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] mm: check pfn_valid first in zero_resv_unavail

On Fri 01-12-17 17:29:51, Dave Young wrote:
> On 12/01/17 at 10:19am, Michal Hocko wrote:
> > On Fri 01-12-17 16:56:57, Dave Young wrote:
> > > On 11/30/17 at 10:35am, Michal Hocko wrote:
> > [...]
> > > > Can we exclude that range from the memblock allocator instead? E.g. what
> > > > happens if somebody allocates from that range?
> > > 
> > > It is a EFI BGRT image buffer provided by firmware, they are reserved
> > > always and can not be used to allocate memory.
> > 
> > Hmm, I see but I was actually suggesting to remove this range from the
> > memblock allocator altogether (memblock_remove) as it shouldn't be there
> > in the first place.
> 
> Oh, I'm not sure because it is introduced as a way for efi to reserve
> boot services areas to be persistent across kexec reboot. See
> drivers/firmware/efi/efi.c: efi_mem_reserve(), BGRT is only one user
> of it, there is esrt and maybe other users, I do not know if it is safe
> :(

Hmm, so it this range ever backed by a valid pfn?
-- 
Michal Hocko
SUSE Labs