[RFC PATCH 2/2] arm: mm: Double logical invert for LPAE pte_write(), pte_dirty()

Russell King - ARM Linux linux at arm.linux.org.uk
Fri Feb 21 06:28:12 EST 2014

On Fri, Feb 14, 2014 at 04:55:13PM +0000, Steve Capper wrote:
> On LPAE, L_PTE_WRITE and L_PTE_DIRTY are in the upper 32-bits.
> Unfortunately, results from pte_write() and pte_dirty() are downcast
> to 32-bits by core code:
>   o gather_stats
>   o huge_pte_dirty
>   o huge_pte_write
>   o make_migration_entry
> This patch adds a double logical invert to pte_write() and pte_dirty()
> for LPAE to ensure that the lower 32-bits are set if true.

We should ensure all those functions return something which is compatible
with "int" correctly.  It didn't matter for non-LPAE as the PTEs fit in
32-bit, but with LPAE, that really needs fixing independently of your
other patch.

FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up.  Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".

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