linux-kernel - Re: [PATCH] efi/arm: fix allocation failure when reserving the kernel base

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Message-Id: <20190821071100.GA26713@rapoport-lnx>
Date:   Wed, 21 Aug 2019 10:11:01 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Chester Lin <clin@...e.com>, Juergen Gross <JGross@...e.com>,
        Joey Lee <JLee@...e.com>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "guillaume.gardet@....com" <guillaume.gardet@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "geert@...ux-m68k.org" <geert@...ux-m68k.org>,
        "ren_guo@...ky.com" <ren_guo@...ky.com>, Gary Lin <GLin@...e.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] efi/arm: fix allocation failure when reserving the
 kernel base

On Wed, Aug 21, 2019 at 09:35:16AM +0300, Ard Biesheuvel wrote:
> On Wed, 21 Aug 2019 at 09:11, Chester Lin <clin@...e.com> wrote:
> >
> > On Tue, Aug 20, 2019 at 03:28:25PM +0300, Ard Biesheuvel wrote:
> > > On Tue, 20 Aug 2019 at 14:56, Russell King - ARM Linux admin
> > > <linux@...linux.org.uk> wrote:
> > > >
> > > > On Fri, Aug 02, 2019 at 05:38:54AM +0000, Chester Lin wrote:
> > > > > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > > > > index f3ce34113f89..909b11ba48d8 100644
> > > > > --- a/arch/arm/mm/mmu.c
> > > > > +++ b/arch/arm/mm/mmu.c
> > > > > @@ -1184,6 +1184,9 @@ void __init adjust_lowmem_bounds(void)
> > > > >               phys_addr_t block_start = reg->base;
> > > > >               phys_addr_t block_end = reg->base + reg->size;
> > > > >
> > > > > +             if (memblock_is_nomap(reg))
> > > > > +                     continue;
> > > > > +
> > > > >               if (reg->base < vmalloc_limit) {
> > > > >                       if (block_end > lowmem_limit)
> > > > >                               /*
> > > >
> > > > I think this hunk is sane - if the memory is marked nomap, then it isn't
> > > > available for the kernel's use, so as far as calculating where the
> > > > lowmem/highmem boundary is, it effectively doesn't exist and should be
> > > > skipped.
> > > >
> > >
> > > I agree.
> > >
> > > Chester, could you explain what you need beyond this change (and my
> > > EFI stub change involving TEXT_OFFSET) to make things work on the
> > > RPi2?
> > >
> >
> > Hi Ard,
> >
> > In fact I am working with Guillaume to try booting zImage kernel and openSUSE
> > from grub2.04 + arm32-efistub so that's why we get this issue on RPi2, which is
> > one of the test machines we have. However we want a better solution for all
> > cases but not just RPi2 since we don't want to affect other platforms as well.
> >
> 
> Thanks Chester, but that doesn't answer my question.
> 
> Your fix is a single patch that changes various things that are only
> vaguely related. We have already identified that we need to take
> TEXT_OFFSET (minus some space used by the swapper page tables) into
> account into the EFI stub if we want to ensure compatibility with many
> different platforms, and as it turns out, this applies not only to
> RPi2 but to other platforms as well, most notably the ones that
> require a TEXT_OFFSET of 0x208000, since they also have reserved
> regions at the base of RAM.
> 
> My question was what else we need beyond:
> - the EFI stub TEXT_OFFSET fix [0]
> - the change to disregard NOMAP memblocks in adjust_lowmem_bounds()
> - what else???

I think the only missing part here is to ensure that non-reserved memory in
bank 0 starts from a PMD-aligned address. I believe this could be done if
EFI stub, but I'm not really familiar with it so this just a semi-educated
guess :)
 
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/commit/?h=next&id=0eb7bad595e52666b642a02862ad996a0f9bfcc0

-- 
Sincerely yours,
Mike.