linux-kernel - Re: Regression (ARM) arch/arm/mm/init.c doesn't build without CONFIG_ARM_PATCH_PHYS

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Message-ID: <52CB2DD2.1070005@ti.com>
Date:	Mon, 6 Jan 2014 17:27:30 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Krzysztof Hałasa <khalasa@...p.pl>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Russell King <rmk+kernel@....linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Regression (ARM) arch/arm/mm/init.c doesn't build without CONFIG_ARM_PATCH_PHYS_VIRT.

On Monday 06 January 2014 05:08 PM, Krzysztof Hałasa wrote:
> Santosh Shilimkar <santosh.shilimkar@...com> writes:
> 
>> I am afraid you didn't understood what the fix is if you say above.
>> arm_dma_limit is broken without this fix for LPAE machines with
>> memory starting 4 GB physical boundary.
> 
> I wonder what CONFIG_ARM_PATCH_PHYS_VIRT and CONFIG_ZONE_DMA do they
> use?
> 
You need to grep where the CONFIG_ARM_PATCH_PHYS_VIRT is used ;)

> Of course, CONFIG_ZONE_DMA must be set, because otherwise the patch
> changes a part disabled with #ifdef. CONFIG_ARM_PATCH_PHYS_VIRT must be
> set because otherwise the kernel will not compile at all.
> 
> Do you accept the fact the configurations with CONFIG_ZONE_DMA and
> without CONFIG_ARM_PATCH_PHYS_VIRT are now broken - by this very commit?
> 
> Now, what "fix" does this commit in its entirety do:
> 
> -     arm_dma_limit = PHYS_OFFSET + arm_dma_zone_size - 1;
> +     arm_dma_limit = __pv_phys_offset + arm_dma_zone_size - 1;
> 
> if under the above circumstances (CONFIG_*) in
> arch/arm/include/asm/memory.h we have:
> 
> extern u64 __pv_phys_offset;
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the only usable declaration of this variable
> extern u64 __pv_offset;
> extern void fixup_pv_table(const void *, unsigned long);
> extern const void *__pv_table_begin, *__pv_table_end;
> 
> #define PHYS_OFFSET __pv_phys_offset
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
Your grep actually missed the assembly files where the actual patching
happens. Please have a look at "arch/arm/kernel/head.S"

The "CONFIG_ARM_PATCH_PHYS_VIRT" is always enabled on almost all ARM builds
since its needed for multi-config kernel to work. May be its time to
make it default enabled but I let Russell comment if there is any
better way to handle this.

Regards,
Santosh

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