linux-kernel - Re: [PATCH] MIPS: Add 48-bit VA space (and 4-level page tables) for 4K pages.

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Message-ID: <20170315133446.GD5512@linux-mips.org>
Date:   Wed, 15 Mar 2017 14:34:46 +0100
From:   Ralf Baechle <ralf@...ux-mips.org>
To:     David Daney <david.daney@...ium.com>
Cc:     linux-mips@...ux-mips.org, James Hogan <james.hogan@...tec.com>,
        linux-kernel@...r.kernel.org, Alex Belits <alex.belits@...ium.com>
Subject: Re: [PATCH] MIPS: Add 48-bit VA space (and 4-level page tables) for
 4K pages.

On Thu, Feb 16, 2017 at 05:27:34PM -0800, David Daney wrote:

> From: Alex Belits <alex.belits@...ium.com>
> 
> Some users must have 4K pages while needing a 48-bit VA space size.
> The cleanest way do do this is to go to a 4-level page table for this
> case.  Each page table level using order-0 pages adds 9 bits to the
> VA size (at 4K pages, so for four levels we get 9 * 4 + 12 == 48-bits.
> 
> For the 4K page size case only we add support functions for the PUD
> level of the page table tree, also the TLB exception handlers get an
> extra level of tree walk.
> 
> Signed-off-by: Alex Belits <alex.belits@...ium.com>
> [david.daney@...ium.com] Forward port to v4.10
> Signed-off-by: David Daney <david.daney@...ium.com>

Thanks folks, queued for 4.12.

While the need for 48-bit address space is not so surprising, the need
for the combination of 4K pages and 48-bit address space is!

I had some minor merge conflicts so it would be good if you could take
a look if https://git.linux-mips.org/cgit/ralf/upstream-sfr.git/commit/?id=afba1896993a0b74aa2ad3076d594e455b3af301
looks good.

  Ralf