tree 7a4e1581e6a698ce488d00d53f348d704e5da7e6
parent 2db2c250dd3d1e74a50d4ab5f44c44ca5cb4e42b
author Benjamin Herrenschmidt <benh@kernel.crashing.org> 1489992543 +1100
committer Michael Ellerman <mpe@ellerman.id.au> 1490691157 +1100

powerpc: Disable HFSCR[TM] if TM is not supported

On Power8 & Power9 the early CPU inititialisation in __init_HFSCR()
turns on HFSCR[TM] (Hypervisor Facility Status and Control Register
[Transactional Memory]), but that doesn't take into account that TM
might be disabled by CPU features, or disabled by the kernel being built
with CONFIG_PPC_TRANSACTIONAL_MEM=n.

So later in boot, when we have setup the CPU features, clear HSCR[TM] if
the TM CPU feature has been disabled. We use CPU_FTR_TM_COMP to account
for the CONFIG_PPC_TRANSACTIONAL_MEM=n case.

Without this a KVM guest might try use TM, even if told not to, and
cause an oops in the host kernel. Typically the oops is seen in
__kvmppc_vcore_entry() and may or may not be fatal to the host, but is
always bad news.

In practice all shipping CPU revisions do support TM, and all host
kernels we are aware of build with TM support enabled, so no one should
actually be able to hit this in the wild.

Fixes: 2a3563b023e5 ("powerpc: Setup in HFSCR for POWER8")
Cc: stable@vger.kernel.org # v3.10+
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Tested-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
[mpe: Rewrite change log with input from Sam, add Fixes/stable]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>