[PATCH 3.16 195/233] KVM: PPC: Book3S HV: Preserve userspace HTM state properly

[Ben Hutchings]

3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Mackerras <paulus@xxxxxxxxxx>

commit 46a704f8409f79fd66567ad3f8a7304830a84293 upstream.

If userspace attempts to call the KVM_RUN ioctl when it has hardware
transactional memory (HTM) enabled, the values that it has put in the
HTM-related SPRs TFHAR, TFIAR and TEXASR will get overwritten by
guest values.  To fix this, we detect this condition and save those
SPR values in the thread struct, and disable HTM for the task.  If
userspace goes to access those SPRs or the HTM facility in future,
a TM-unavailable interrupt will occur and the handler will reload
those SPRs and re-enable HTM.

If userspace has started a transaction and suspended it, we would
currently lose the transactional state in the guest entry path and
would almost certainly get a "TM Bad Thing" interrupt, which would
cause the host to crash.  To avoid this, we detect this case and
return from the KVM_RUN ioctl with an EINVAL error, with the KVM
exit reason set to KVM_EXIT_FAIL_ENTRY.

Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08)
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/powerpc/kvm/book3s_hv.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1802,6 +1802,27 @@ static int kvmppc_vcpu_run_hv(struct kvm
 		return -EINVAL;
 	}
 
+	/*
+	 * Don't allow entry with a suspended transaction, because
+	 * the guest entry/exit code will lose it.
+	 * If the guest has TM enabled, save away their TM-related SPRs
+	 * (they will get restored by the TM unavailable interrupt).
+	 */
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	if (cpu_has_feature(CPU_FTR_TM) && current->thread.regs &&
+	    (current->thread.regs->msr & MSR_TM)) {
+		if (MSR_TM_ACTIVE(current->thread.regs->msr)) {
+			run->exit_reason = KVM_EXIT_FAIL_ENTRY;
+			run->fail_entry.hardware_entry_failure_reason = 0;
+			return -EINVAL;
+		}
+		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
+
 	kvmppc_core_prepare_to_enter(vcpu);
 
 	/* No need to go into the guest when all we'll do is come back out */