** Changed in: linux (Ubuntu)
   Importance: Undecided => Medium

** Tags removed: targetmilestone-inin---
** Tags added: kernel-da-key targetmilestone-inin---ppc64el

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  remap_4K_pfn() safety improvement needed for Ubuntu 14.10

Status in “linux” package in Ubuntu:

Bug description:
  == Comment: #0 - Brian Hart <ha...@us.ibm.com> - 2014-08-04 17:41:57 ==
  ---Problem Description---
  The current implementation of remap_4k_pfn() trusts that it's safe to map the 
PFN supplied by the requestor.  But there may be PFNs that are not safe to map 
via remap_4k_pfn().  (For example, the addresses at which PCI MMIO regions are 
mapped in some hypervisor configurations.)  When an unsafe PFN passes through 
remap_4k_pfn() some address bits may be unknowingly dropped by the underlying 
remapping routines.  When that happens the remap will appear to succeed, but 
any later attempt to use the mapping will checkstop the machine because the 
truncated target address is not present in the machine.

  A patch has been submitted that will cause remap_4k_pfn() to detect
  and reject these unsafe requests:


  Our project needs some form of this safety improvement in the Ubuntu 14.10 
  ---uname output---
  Linux tul115p1 3.16.0-6-generic #11-Ubuntu SMP Mon Jul 28 02:00:45 UTC 2014 
ppc64le ppc64le ppc64le GNU/Linux
  Machine Type = 8286-42A 
  A debugger is not configured
  ---Steps to Reproduce---
   The problem requires a hypervisor that allows PCI MMIO regions to span above 
the 46-bit line, and a device driver that maps MMIO regions using 

  I can provide detailed instructions and a driver upon request.
  Stack trace output:
  Oops output:
  System Dump Info:
    The system is not configured to capture a system dump.

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