On Thu, 2016-12-05 at 11:26:44 UTC, Thomas Huth wrote:

The SIAR and SDAR registers are available twice, one time as SPRs
780 / 781 (unprivileged, but read-only), and one time as the SPRs
796 / 797 (privileged, but read and write). The Linux kernel code
currently uses the unprivileged  SPRs - while this is OK for reading,
writing to that register of course does not work.
Since the KVM code tries to write to this register, too (see the mtspr
in book3s_hv_rmhandlers.S), the contents of this register sometimes get
lost for the guests, e.g. during migration of a VM.
To fix this issue, simply switch to the privileged SPR numbers instead.

Signed-off-by: Thomas Huth <redacted>
Acked-by: Paul Mackerras <redacted>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/d23fac2b27d94aeb7b65536a50

cheers