linux-kernel - Re: [PATCH] arm: skip nomap memblocks while finding the lowmem/highmem boundary

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Date:   Thu, 22 Aug 2019 09:46:50 +0300
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Chester Lin <clin@...e.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "geert@...ux-m68k.org" <geert@...ux-m68k.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "guillaume.gardet@....com" <guillaume.gardet@....com>,
        Gary Lin <GLin@...e.com>, Joey Lee <JLee@...e.com>
Subject: Re: [PATCH] arm: skip nomap memblocks while finding the
 lowmem/highmem boundary

On Thu, 22 Aug 2019 at 09:44, Mike Rapoport <rppt@...ux.ibm.com> wrote:
>
> On Thu, Aug 22, 2019 at 03:59:42AM +0000, Chester Lin wrote:
> > On Thu, Aug 22, 2019 at 11:45:34AM +0800, Chester Lin wrote:
> > > adjust_lowmem_bounds() checks every memblocks in order to find the boundary
> > > between lowmem and highmem. However some memblocks could be marked as NOMAP
> > > so they are not used by kernel, which should be skipped while calculating
> > > the boundary.
> > >
> > > Signed-off-by: Chester Lin <clin@...e.com>
> > > ---
> > >  arch/arm/mm/mmu.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > > index 426d9085396b..b86dba44d828 100644
> > > --- a/arch/arm/mm/mmu.c
> > > +++ b/arch/arm/mm/mmu.c
> > > @@ -1181,6 +1181,9 @@ 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)
> > >                             /*
> > > --
> > > 2.22.0
> > >
> >
> > Hi Russell, Mike and Ard,
> >
> > Per the discussion in the thread "[PATH] efi/arm: fix allocation failure ...",
> > (https://lkml.org/lkml/2019/8/21/163), I presume that the change to disregard
> > NOMAP memblocks in adjust_lowmem_bounds() should be separated as a single patch.
> >
> > Please let me know if any suggestion, thank you.
>
> Let's add this one to the series:
>
> From 06a986e79d60c310c804b3e550bd50316597aec5 Mon Sep 17 00:00:00 2001
> From: Mike Rapoport <rppt@...ux.ibm.com>
> Date: Thu, 22 Aug 2019 09:27:40 +0300
> Subject: [PATCH] arm: ensure that usable memory in bank 0 starts from a
>  PMD-aligned address
>
> The calculation of memblock_limit in adjust_lowmem_bounds() assumes that
> bank 0 starts from a PMD-aligned address. However, the beginning of the
> first bank may be NOMAP memory and the start of usable memory
> will be not aligned to PMD boundary. In such case the memblock_limit will
> be set to the end of the NOMAP region, which will prevent any memblock
> allocations.
>
> Mark the region between the end of the NOMAP area and the next PMD-aligned
> address as NOMAP as well, so that the usable memory will start at
> PMD-aligned address.
>
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>

Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

> ---
>  arch/arm/mm/mmu.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 4495a26..25da9b2 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1177,6 +1177,22 @@ 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)) {
> +                       if (!IS_ALIGNED(reg->base, PMD_SIZE)) {
> +                               phys_addr_t len;
> +
> +                               len = round_up(reg->base, PMD_SIZE) - reg->base;
> +                               memblock_mark_nomap(reg->base, len);
> +                       }
> +                       break;
> +               }
> +       }
> +
>         for_each_memblock(memory, reg) {
>                 phys_addr_t block_start = reg->base;
>                 phys_addr_t block_end = reg->base + reg->size;
> --
> 2.7.4
>
>
> --
> Sincerely yours,
> Mike.
>