Re: [PATCH] kdump: don't call __ioremap() for pfn = 0

Michael Ellerman wrote:

quoted

Attached is a patch to fix this problem. During such rare cases don't call
__ioremap() to do the address translation, instead use __va() .
    

It's not really rare, it's just when we're reading /dev/oldmem directly.
  

That's true. Since we don't try to copy raw dump from /dev/oldmem very
often, we haven't come across this problem. Hence rare .. but as
michael said always recreatable while using dd command with /dev/oldmem.

We can actually use the __va() trick for the whole linear mapping rather
than just pfn 0, which saves the ioremap. We also shouldn't really be
trying to iounmap(__va(0)).
  

Yes. Makes sense. Agreed.

So perhaps something more like this? Although it's a bit ugly because of
the need to conditionally call iounmap().
  

< snip > 

Thanks
-Sachin