linux-kernel - Re: [PATCH 1/2] ARM: Pass IFSR register to do

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Date:	Sun, 20 Sep 2009 09:15:50 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Bityutskiy Artem <Artem.Bityutskiy@...ia.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Koskinen Aaro <aaro.koskinen@...ia.com>
Subject: Re: [PATCH 1/2] ARM: Pass IFSR register to do_PrefetchAbort()

On Sat, Sep 19, 2009 at 12:03:16PM +0100, Russell King - ARM Linux wrote:
> On Fri, Sep 18, 2009 at 11:55:42PM +0300, Kirill A. Shutemov wrote:
> > It needed for proper prefetch abort handling on ARMv7.
> 
> I think the only thing which is missing is an explaination about why
> this is desirable given that only later CPUs can give this additional
> information.

So you've posted it to the patch system, without further discussion here.

I think the solution is wrong - it makes instruction permission faults
unnecessarily noisy, which is not what the decoding table is supposed
to be doing.  The decoding table's bad entries are there to catch those
_unexpected_ cases.

Instead, I suggest that you have a look at this:

        if (fsr & (1 << 11)) /* write? */
                mask = VM_WRITE;
        else
                mask = VM_READ|VM_EXEC|VM_WRITE;

        fault = VM_FAULT_BADACCESS;
        if (!(vma->vm_flags & mask))
                goto out;

in __do_page_fault - if we are handling a prefetch abort, we really only
want to check that the VMA has VM_EXEC permission, not that it can be
read and written as well.
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