linux-kernel - Re: [PATCH v7 09/16] ARM: LPAE: MMU setup for the 3-level page table format

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Date:	Fri, 19 Aug 2011 12:10:54 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Ian Campbell <ijc@...lion.org.uk>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"tim@....org" <tim@....org>
Subject: Re: [PATCH v7 09/16] ARM: LPAE: MMU setup for the 3-level page
 table format

On Fri, Aug 19, 2011 at 11:25:57AM +0100, Ian Campbell wrote:
> On Wed, 2011-08-10 at 16:03 +0100, Catalin Marinas wrote:
> > +/*
> > + *     cpu_v7_set_pte_ext(ptep, pte)
> > + *
> > + *     Set a level 2 translation table entry.
> > + *
> > + *     - ptep  - pointer to level 2 translation table entry
> > + *               (hardware version is stored at +2048 bytes)
> 
> +2048 thing not true for LPAE?
> 
> > + *     - pte   - PTE value to store
> > + *     - ext   - value for extended PTE bits
> 
> "ext" is not actually present/used in this variant, rather pte is split
> between r1 and r2?

Yes, you are right, the comments have just been copied from proc-v7.S.
I'll go through them again make sure they are still valid.

> > + */
> > +ENTRY(cpu_v7_set_pte_ext)
> > +#ifdef CONFIG_MMU
> > +       tst     r2, #L_PTE_PRESENT
> > +       beq     1f
> > +       tst     r3, #1 << (55 - 32)             @ L_PTE_DIRTY
> > +       orreq   r2, #L_PTE_RDONLY
> > +1:     strd    r2, r3, [r0]
> 
> AIUI this 64-bit store is not atomic. Is there something about the ARM
> architecture which would prevent the MMU prefetching the half written
> entry and caching it in the TLB?

CPU implementations that include LPAE guarantee the atomicity of a
double-word store (STRD) if the alignment is correct.

Thanks.

-- 
Catalin
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