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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Wed, 21 Aug 2019 12:42:56 +0300
Message-ID: <CAKv+Gu91d3NrcEGsz6yapVnf3NV=F-cGeftdPo=H-cNTXCC2EA@mail.gmail.com>
Subject: Re: [PATCH] efi/arm: fix allocation failure when reserving the kernel base
To:     Mike Rapoport <rppt@linux.ibm.com>
Cc:     Chester Lin <clin@suse.com>, Juergen Gross <JGross@suse.com>,
        Joey Lee <JLee@suse.com>,
        "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
        "guillaume.gardet@arm.com" <guillaume.gardet@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Russell King - ARM Linux admin <linux@armlinux.org.uk>,
        "geert@linux-m68k.org" <geert@linux-m68k.org>,
        "ren_guo@c-sky.com" <ren_guo@c-sky.com>, Gary Lin <GLin@suse.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "mingo@kernel.org" <mingo@kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
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On Wed, 21 Aug 2019 at 11:29, Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Wed, Aug 21, 2019 at 10:29:37AM +0300, Ard Biesheuvel wrote:
> > On Wed, 21 Aug 2019 at 10:11, Mike Rapoport <rppt@linux.ibm.com> wrote:
> > >
...
> > > 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 :)
> > >
> >
> > Given that it is the ARM arch code that imposes this requirement, how
> > about adding something like this to adjust_lowmem_bounds():
> >
> > if (memblock_start_of_DRAM() % PMD_SIZE)
> >     memblock_mark_nomap(memblock_start_of_DRAM(),
> >         PMD_SIZE - (memblock_start_of_DRAM() % PMD_SIZE));
>
> memblock_start_of_DRAM() won't work here, as it returns the actual start of
> the DRAM including NOMAP regions. Moreover, as we cannot mark a region
> NOMAP inside for_each_memblock() this should be done beforehand.
>
> I think something like this could work:
>
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 2f0f07e..f2b635b 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1178,6 +1178,19 @@ void __init adjust_lowmem_bounds(void)
>          */
>         vmalloc_limit = (u64)(uintptr_t)vmalloc_min - PAGE_OFFSET + PHYS_OFFSET;
>
> +       /*
> +        * The first usable region must be PMD aligned. Mark its start
> +        * as MEMBLOCK_NOMAP if it isn't
> +        */
> +       for_each_memblock(memory, reg) {
> +               if (!memblock_is_nomap(reg) && (reg->base % PMD_SIZE)) {
> +                       phys_addr_t size = PMD_SIZE - (reg->base % PMD_SIZE);
> +
> +                       memblock_mark_nomap(reg->base, size);
> +                       break;

We should break on the first !NOMAP memblock, even if it is already
PMD aligned, but beyond that, this looks ok to me.