From: catalin.marinas@arm•com (Catalin Marinas)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V4 2/2] arm: mm: Switch back to L_PTE_WRITE
Date: Mon, 23 Jun 2014 12:17:19 +0100 [thread overview]
Message-ID: <20140623111719.GD15907@arm.com> (raw)
In-Reply-To: <20140620181748.GW32514@n2100.arm.linux.org.uk>
On Fri, Jun 20, 2014 at 07:17:48PM +0100, Russell King - ARM Linux wrote:
> On Mon, Jun 16, 2014 at 03:32:39PM +0100, Steve Capper wrote:
> > For LPAE, we have the following means for encoding writable or dirty
> > ptes:
> > L_PTE_DIRTY L_PTE_RDONLY
> > !pte_dirty && !pte_write 0 1
> > !pte_dirty && pte_write 0 1
> > pte_dirty && !pte_write 1 1
> > pte_dirty && pte_write 1 0
> >
> > So we can't distinguish between writable clean ptes and read only
> > ptes. This can cause problems with ptes being incorrectly flagged as
> > read only when they are writable but not dirty.
> >
> > This patch re-introduces the L_PTE_WRITE bit for both short descriptors
> > and long descriptors, by reverting
> > 36bb94b ARM: pgtable: provide RDONLY page table bit rather than WRITE bit
[...]
> So, what I say is why not, for the troublesome 3-level case:
>
> - Assign bit 58 for L_PTE_RDONLY
> - Convert the state of bit 58 and L_PTE_DIRTY to the AP[2] bit:
>
> ubfx ip, rh, #(58 - 32) @ L_PTE_RDONLY
> bfi rl, ip, #7, #1 @ PTE_AP2
> tst rh, #1 << (55 - 32) @ L_PTE_DIRTY
> orreq rl, #PTE_AP2
>
> This means we keep the read-only terminology, which is much more
> understandable when reading the assembly code than what we had when
> we used the write terminology.
Good idea. This seems to be even better resulting in a simpler patch.
--
Catalin
next prev parent reply other threads:[~2014-06-23 11:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-16 14:32 [PATCH V4 0/2] PTE fixes for ARM LPAE Steve Capper
2014-06-16 14:32 ` [PATCH V4 1/2] arm: mm: Introduce {pte, pmd}_isset and {pte, pmd}_isclear Steve Capper
2014-06-20 9:12 ` [PATCH V4 1/2] arm: mm: Introduce {pte,pmd}_isset and {pte,pmd}_isclear Will Deacon
2014-06-20 10:04 ` Russell King - ARM Linux
2014-06-16 14:32 ` [PATCH V4 2/2] arm: mm: Switch back to L_PTE_WRITE Steve Capper
2014-06-20 9:21 ` Will Deacon
2014-06-20 13:23 ` Steve Capper
2014-06-20 18:17 ` Russell King - ARM Linux
2014-06-23 11:17 ` Catalin Marinas [this message]
2014-06-23 15:07 ` Steve Capper
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