linux-kernel - Re: [PATCH] arm64: mm: Fix memmap to be initialized for the entire section

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Date:   Thu, 24 Nov 2016 20:26:59 +0100
From:   Robert Richter <robert.richter@...ium.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC:     Will Deacon <will.deacon@....com>,
        Robert Richter <rric@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        David Daney <david.daney@...ium.com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: mm: Fix memmap to be initialized for the entire
 section

Ard,

> > >> On 24 November 2016 at 13:51, Robert Richter <robert.richter@...ium.com> wrote:
> > >> > On 24.11.16 13:44:31, Ard Biesheuvel wrote:

> > >> Regions containing firmware tables are owned by the firmware, and it
> > >> is the firmware that tells us which memory attributes we are allowed
> > >> to use. If those attributes include WB, it is perfectly legal to use a
> > >> cacheable mapping. That does *not* mean they should be covered by the
> > >> linear mapping. The linear mapping is read-write-non-exec, for
> > >> instance, and we may prefer to use a read-only mapping and/or
> > >> executable mapping.
> > >
> > > Ok, I am going to fix try_ram_remap().

I revisited the code and it is working well already since:

 e7cd190385d1 arm64: mark reserved memblock regions explicitly in iomem

Now, try_ram_remap() is only called if the region to be mapped is
entirely in IORESOURCE_SYSTEM_RAM. This is only true for normal mem
ranges and not NOMAP mem. region_intersects() then returns
REGION_INTERSECTS and calls try_ram_remap(). For the NOMAP memory case
REGION_DISJOINT would be returned and thus arch_memremap_wb() being
called directly. Before the e7cd190385d1 change try_ram_remap() was
called also for nomap regions.

So we can leave memremap() as it is and just apply this patch
unmodified. What do you think? Please ack.

I am going to prepare the pfn_is_ram() change in addition to this
patch, but that should not be required for this fix to work correcly.

Thanks,

-Robert