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Re: [Qemu-devel] [PATCH v2 3/3] target-arm: get_phys_addr_lpae: more xn

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH v2 3/3] target-arm: get_phys_addr_lpae: more xn control
Date: Wed, 11 Mar 2015 18:36:51 +0000

On 11 March 2015 at 18:30, Andrew Jones <address@hidden> wrote:
> My interpretation of SCTLR_EL1.WXN was just wrong. There is
> talks about "EL1&0"

That's just the name of the translation regime (ie
there's a shared set of page tables that handle
translation for both EL1 and EL0).

> and I assumed it meant that when WXN is
> on, then both EL1 and EL0 should lose executability.

No; and you can see an example of this in the table:
UXN=0, PXN=0, AP[2:1] = 00, WXN=0 is RWX for EL1 and
X for EL0. Setting WXN changes the EL1 rights to just
RW (because the page is writable there) but leaves the
EL0 rights as X (because there the page is not writable).

> However
> it can certainly be interpreted as applying to them both, but
> based on their respective access permissions, which is how
> I guess I should have interpreted it.

Yes, this is the correct interpretation.

-- PMM

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