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

    KVM: PPC: Book3S HV: Reload HTM registers explicitly

to the 4.4-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-reload-htm-registers-explicitly.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let [off-list ref] know about it.

From paulus@ozlabs.org  Thu Aug  3 12:20:26 2017

From: Paul Mackerras <redacted>
Date: Mon, 31 Jul 2017 10:43:37 +1000
Subject: KVM: PPC: Book3S HV: Reload HTM registers explicitly
To: stable@vger.kernel.org
Message-ID: [ref]
Content-Disposition: inline

From: Paul Mackerras <redacted>

Commit 46a704f8409f ("KVM: PPC: Book3S HV: Preserve userspace HTM
state properly", 2017-06-15) added code which assumes that the kernel
is able to handle a TM (transactional memory) unavailable interrupt
from userspace by reloading the TM-related registers and enabling TM
for the process.  That ability was added in the 4.9 kernel; earlier
kernel versions simply panic on getting the TM unavailable interrupt.

Since commit 46a704f8409f has been backported to the 4.4 stable tree
as commit 824b9506e4f2, 4.4.75 and subsequent versions are vulnerable
to a userspace-triggerable panic.

This patch fixes the problem by explicitly reloading the TM-related
registers before returning to userspace, rather than disabling TM
for the process.

Commit 46a704f8409f also failed to enable TM for the kernel, leading
to a TM unavailable interrupt in the kernel, causing an oops.  This
fixes that problem too, by enabling TM before accessing the TM
registers.  That problem is fixed upstream by the patch "KVM: PPC:
Book3S HV: Enable TM before accessing TM registers".

Fixes: 824b9506e4f2 ("KVM: PPC: Book3S HV: Preserve userspace HTM state properly")
Signed-off-by: Paul Mackerras <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/powerpc/kvm/book3s_hv.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c

@@ -2711,10 +2711,11 @@ static int kvmppc_vcpu_run_hv(struct kvm
 			run->fail_entry.hardware_entry_failure_reason = 0;
 			return -EINVAL;
 		}
+		/* Enable TM so we can read the TM SPRs */
+		mtmsr(mfmsr() | MSR_TM);
 		current->thread.tm_tfhar = mfspr(SPRN_TFHAR);
 		current->thread.tm_tfiar = mfspr(SPRN_TFIAR);
 		current->thread.tm_texasr = mfspr(SPRN_TEXASR);
-		current->thread.regs->msr &= ~MSR_TM;
 	}
 #endif
 

@@ -2782,6 +2783,19 @@ static int kvmppc_vcpu_run_hv(struct kvm
 	}
 	mtspr(SPRN_VRSAVE, user_vrsave);
 
+	/*
+	 * Since we don't do lazy TM reload, we need to reload
+	 * the TM registers here.
+	 */
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	if (cpu_has_feature(CPU_FTR_TM) && current->thread.regs &&
+	    (current->thread.regs->msr & MSR_TM)) {
+		mtspr(SPRN_TFHAR, current->thread.tm_tfhar);
+		mtspr(SPRN_TFIAR, current->thread.tm_tfiar);
+		mtspr(SPRN_TEXASR, current->thread.tm_texasr);
+	}
+#endif
+
  out:
 	vcpu->arch.state = KVMPPC_VCPU_NOTREADY;
 	atomic_dec(&vcpu->kvm->arch.vcpus_running);

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

queue-4.4/kvm-ppc-book3s-hv-save-restore-host-values-of-debug-registers.patch
queue-4.4/kvm-ppc-book3s-hv-context-switch-ebb-registers-properly.patch
queue-4.4/kvm-ppc-book3s-hv-restore-critical-sprs-to-host-values-on-guest-exit.patch
queue-4.4/kvm-ppc-book3s-hv-reload-htm-registers-explicitly.patch