Patch "KVM: PPC: Book3S HV: Ignore timebase offset on POWER9 DD1" has been added to the 4.11-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KVM: PPC: Book3S HV: Ignore timebase offset on POWER9 DD1

to the 4.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-ppc-book3s-hv-ignore-timebase-offset-on-power9-dd1.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 3d3efb68c19e539f0535c93a5258c1299270215f Mon Sep 17 00:00:00 2001
From: Paul Mackerras <paulus@ozlabs.org>
Date: Tue, 6 Jun 2017 14:35:30 +1000
Subject: KVM: PPC: Book3S HV: Ignore timebase offset on POWER9 DD1

From: Paul Mackerras <paulus@ozlabs.org>

commit 3d3efb68c19e539f0535c93a5258c1299270215f upstream.

POWER9 DD1 has an erratum where writing to the TBU40 register, which
is used to apply an offset to the timebase, can cause the timebase to
lose counts.  This results in the timebase on some CPUs getting out of
sync with other CPUs, which then results in misbehaviour of the
timekeeping code.

To work around the problem, we make KVM ignore the timebase offset for
all guests on POWER9 DD1 machines.  This means that live migration
cannot be supported on POWER9 DD1 machines.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/kvm/book3s_hv.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1481,6 +1481,14 @@ static int kvmppc_set_one_reg_hv(struct
 		r = set_vpa(vcpu, &vcpu->arch.dtl, addr, len);
 		break;
 	case KVM_REG_PPC_TB_OFFSET:
+		/*
+		 * POWER9 DD1 has an erratum where writing TBU40 causes
+		 * the timebase to lose ticks.  So we don't let the
+		 * timebase offset be changed on P9 DD1.  (It is
+		 * initialized to zero.)
+		 */
+		if (cpu_has_feature(CPU_FTR_POWER9_DD1))
+			break;
 		/* round up to multiple of 2^24 */
 		vcpu->arch.vcore->tb_offset =
 			ALIGN(set_reg_val(id, *val), 1UL << 24);


Patches currently in stable-queue which might be from paulus@ozlabs.org are

queue-4.11/kvm-ppc-book3s-hv-preserve-userspace-htm-state-properly.patch
queue-4.11/kvm-ppc-book3s-hv-cope-with-host-using-large-decrementer-mode.patch
queue-4.11/kvm-ppc-book3s-hv-save-restore-host-values-of-debug-registers.patch
queue-4.11/kvm-ppc-book3s-hv-context-switch-ebb-registers-properly.patch
queue-4.11/kvm-ppc-book3s-hv-ignore-timebase-offset-on-power9-dd1.patch
queue-4.11/kvm-ppc-book3s-hv-restore-critical-sprs-to-host-values-on-guest-exit.patch