kernel bug in "Drop WIMG in favour of new constants"?

[Balbir Singh]

On 16/06/16 14:33, Darrick J. Wong wrote:
> Hi Aneesh,
> 
> I noticed when trying out 4.7-rc3 on qemu-2.5 that the kernel no longer
> boots.  4.6 booted just fine, so I bisected the kernel to the commit
> 30bda41aba4efb2370c97e2cbe7385de93ccc372, which is "powerpc/mm: Drop WIMG in
> favour of new constants".  The changelog suggests that the KVM changes need
> closer review, and here's an actual crash:
> 
> (I can send libvirt's machine xml, .config, and full dmesg if that helps.)
> 
> --Darrick


Looking at the address - 0xd000080080000010, looks like map_kernel_page followed
by a fault here did not do the right thing. This EA range belongs to the io_remap
range, IIUC. The only suspicious bits I could find are

+       /*
+        * if host is mapped cache inhibited, make sure hptel also have
+        * cache inhibited.
+        */
+       if (wimg & HPTE_R_W) /* FIXME!! is this ok for all guest. ? */
+               return false;


Aneesh also posted some changes to hpte_update and hpte_updatepp that might be
interesting

Balbir