Re: [PATCH 2/2] arm64:acpi Fix the acpi alignment exeception when 'mem=' specified

[Dennis Chen <dennis.chen@arm.com>]

On Thu, Jun 23, 2016 at 01:42:30PM +0100, Mark Rutland wrote:
> On Thu, Jun 23, 2016 at 07:30:15PM +0800, Dennis Chen wrote:
> > This is a rework patch based on [1]. According to the proposal from
> > Mark Rutland, when applying the system memory limit through 'mem=x'
> > kernel command line, don't remove the rest memory regions above the
> > limit from the memblock, instead marking them as MEMBLOCK_NOMAP region,
> > which will preserve the ability to identify regions as normal memory
> > while not using them for allocation and the linear map.
> > 
> > Without this patch, the ACPI core will map those acpi data regions(if
> > they are above the limit) as device type memory, which will result in
> > the alignment exception when ACPI core parses the AML data stream 
> > since the parsing will produce some non-alignment accesses.
> >
> > [1]:http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/438443.html
> 
> Please rewrite the message to be standalone (i.e. so peopel can read
> this without having to folow the link).
> 
> Explain why using mem= makes ACPI think regions should be mapped as
> Device memory, the problems this causes for ACPICA, then cover why we
> want to nomap the region.
> 
> > Signed-off-by: Dennis Chen <dennis.chen@arm.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Steve Capper <steve.capper@arm.com>
> > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > Cc: Will Deacon <will.deacon@arm.com>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Cc: Matt Fleming <matt@codeblueprint.co.uk>
> > Cc: linux-mm@kvack.org
> > Cc: linux-acpi@vger.kernel.org
> > Cc: linux-efi@vger.kernel.org
> > ---
> >  arch/arm64/mm/init.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index d45f862..e509e24 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -222,12 +222,14 @@ void __init arm64_memblock_init(void)
> >  
> >  	/*
> >  	 * Apply the memory limit if it was set. Since the kernel may be loaded
> > -	 * high up in memory, add back the kernel region that must be accessible
> > -	 * via the linear mapping.
> > +	 * in the memory regions above the limit, so we need to clear the
> > +	 * MEMBLOCK_NOMAP flag of this region to make it can be accessible via
> > +	 * the linear mapping.
> >  	 */
> >  	if (memory_limit != (phys_addr_t)ULLONG_MAX) {
> > -		memblock_enforce_memory_limit(memory_limit);
> > -		memblock_add(__pa(_text), (u64)(_end - _text));
> > +		memblock_mem_limit_mark_nomap(memory_limit);
> > +		if (!memblock_is_map_memory(__pa(_text)))
> > +			memblock_clear_nomap(__pa(_text), (u64)(_end - _text));
> 
> I think that the memblock_is_map_memory() check should go. Just because
> a page of the kernel image is mapped doesn't mean that the rest is. That
> will make this a 1-1 change.
>
Good catch! Will be applied, thanks!
> 
> Other than that, this looks right to me.
> 
> Thanks,
> Mark.
> 
> >  	}
> >  
> >  	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) {
> > -- 
> > 1.8.3.1
> > 
> 

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