linux-kernel - Re: [PATCH 7/8 linux-next] mm: warn about possible alignment problem

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Date:   Fri, 2 Dec 2016 11:52:18 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Fabian Frederick <fabf@...net.be>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/8 linux-next] mm: warn about possible alignment problem

On Fri, Dec 2, 2016 at 11:22 AM, Fabian Frederick <fabf@...net.be> wrote:
> Commit 5f29a77cd957
> ("mm: fix mixed zone detection in devm_memremap_pages")
> Aligned resource limits before region_intersects() which breaks
> the following with false assertions on kernel command line: memmap=4M!700M
>
> "devm_memremap_pages attempted on mixed region [ mem 0x2bc00000-0x2bfffff
> flags 0x200]"
>
> Memory regions
> 0x100000-0x2bbfffff: usable
> 0x2bc000000-0x2bbfffff: persistent
> 0x2c0000000-0x2bffffff: usable
>
> resource start: 0x2bc00000
> align start:    0x28000000
> resource size:  0x3fffffff
> align size:     0x80000000
> SECTION_SIZE:    0x8000000
>
> Now we need aligned memmap declarations based on 128M in this case
> eg memmap=128!640M
>
> Signed-off-by: Fabian Frederick <fabf@...net.be>
> ---
>  kernel/memremap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index b501e39..1bb5eec 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -296,8 +296,8 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
>                 IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE);
>
>         if (is_ram == REGION_MIXED) {
> -               WARN_ONCE(1, "%s attempted on mixed region %pr\n",
> -                               __func__, res);
> +               WARN_ONCE(1, "%s attempted on mixed region %pr or arguments not aligned to section size: %#lx\n",
> +                               __func__, res, SECTION_SIZE);
>                 return ERR_PTR(-ENXIO);
>         }

This should be addressed by the sub-section hotplug patches:

"[PATCH 00/11] mm: sub-section memory hotplug support"
https://lkml.org/lkml/2016/12/1/740