On Tue, Jun 14, 2011 at 10:07 PM, Timur Tabi [off-list ref] wrote:

Timur Tabi wrote:

quoted

Hmmm.... I find that surprising. =A0Memory allocated via ioremap() is su=

pposed to

quoted

be available in interrupt handlers, where TLB mappings can't be created
on-the-fly. =A0I'm not sure that your observation is correct.

Ok, it turns out I'm wrong. =A0As long as the page is in the page tables =

(i.e.

physically present in RAM), you can take a TLB miss in an interrupt handl=

er, and

the TLB miss handler will create a TLB for you.

This means that ...

quoted

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 unsigned long dummy =3D =

*(volatile unsigned long *)p;

quoted

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (void)dummy;
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 }

* After these changes (make sure all code is mapped + make sure to
read all pages so that the TLBs are updated), my scenario works fine.

is not going to work reliably, because it assumes that the TLBs created b=

y your

multiple ioremap() calls will still be there when your code is called.

If you use just a single ioremap() call, but still touch every page, that=

 should

work for you just as well.

I am using a single __ioremap call.
You have a point about the reliability of this: if an interrupt occurs
between the mapping or dummy reading, and the point where the actual
code is executing, some TLB entries may have been replaced, right?
I think I can make it more reliable by dummy reading the pages *after*
I disabled interrupts on that processor, immediately before jumping to
the boot code. Is that correct?
(note that I have to disable interrupts anyhow for the boot code to
work properly without interruptions to 'linux land'.

Thanks for your input,
Thomas