Re: [PATCH 2/6] 8xx: get rid of _PAGE_HWWRITE dependency in MMU.

On Thu, 2009-10-08 at 00:08 +0200, Joakim Tjernlund wrote:

Benjamin Herrenschmidt [off-list ref] wrote on 07/10/2009 23:14:52:

quoted

On Wed, 2009-10-07 at 22:46 +0200, Joakim Tjernlund wrote:

quoted

+   andi.   r11, r10, _PAGE_USER | _PAGE_ACCESSED
+   cmpwi   cr0, r11, _PAGE_USER | _PAGE_ACCESSED
+   bne-   cr0, 2f

Did you mean _PAGE_PRESENT | _PAGE_ACCESSED ?

quoted

+2:
+   mfspr   r11, SRR1
+   rlwinm   r11, r11, 0, 5, 3 /* clear guarded */
+   mtspr   SRR1, r11

What is the above for ?

TLB Miss will set that bit unconditionally and that is
the same bit as protection error in TLB error.

And ? Big deal :-) IE. Once you get to InstructionAccess, it doesn't
matter if that bit is set, does it ?

Lets start simple, shall we? :)
Anyhow, I looked some more at that and I don't the best thing is
to use shifts. All bits are correct if you invert RW and add an exception
for extended coding.

Right, as long as you avoid doing a conditional branch :-)

Because if you go to C with a protection fault, you are in trouble.

Why ?

So deal with it here. Now, I got another idea too that will make this go away
if it work out

I don't understand your point about protection faults.

You should be able to go straight to C with -anything-, that's what I do
for all other platforms.

Ben.