KVM: PPC: Book3S HV P9: Fix guest TM support

The conversion to C introduced several bugs in TM handling that can
cause host crashes with TM bad thing interrupts. Mostly just simple
typos or missed logic in the conversion that got through due to my
not testing TM in the guest sufficiently.

- Early TM emulation for the softpatch interrupt should be done if fake
  suspend mode is _not_ active.

- Early TM emulation wants to return immediately to the guest so as to
  not doom transactions unnecessarily.

- And if exiting from the guest, the host MSR should include the TM[S]
  bit if the guest was T/S, before it is treclaimed.

After this fix, all the TM selftests pass when running on a P9 processor
that implements TM with softpatch interrupt.

Fixes: 89d35b23 ("KVM: PPC: Book3S HV P9: Implement the rest of the P9 path in C")
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210712013650.376325-1-npiggin@gmail.com

arch/powerpc/kvm/book3s_hv_p9_entry.c

@@ -317,6 +317,9 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	 */
 	mtspr(SPRN_HDEC, hdec);
 
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+tm_return_to_guest:
+#endif
 	mtspr(SPRN_DAR, vcpu->arch.shregs.dar);
 	mtspr(SPRN_DSISR, vcpu->arch.shregs.dsisr);
 	mtspr(SPRN_SRR0, vcpu->arch.shregs.srr0);
@@ -415,11 +418,23 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 		 * is in real suspend mode and is trying to transition to
 		 * transactional mode.
 		 */
-		if (local_paca->kvm_hstate.fake_suspend &&
+		if (!local_paca->kvm_hstate.fake_suspend &&
 				(vcpu->arch.shregs.msr & MSR_TS_S)) {
 			if (kvmhv_p9_tm_emulation_early(vcpu)) {
-				/* Prevent it being handled again. */
-				trap = 0;
+				/*
+				 * Go straight back into the guest with the
+				 * new NIP/MSR as set by TM emulation.
+				 */
+				mtspr(SPRN_HSRR0, vcpu->arch.regs.nip);
+				mtspr(SPRN_HSRR1, vcpu->arch.shregs.msr);
+
+				/*
+				 * tm_return_to_guest re-loads SRR0/1, DAR,
+				 * DSISR after RI is cleared, in case they had
+				 * been clobbered by a MCE.
+				 */
+				__mtmsrd(0, 1); /* clear RI */
+				goto tm_return_to_guest;
 			}
 		}
 #endif
@@ -499,6 +514,10 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	 * If we are in real mode, only switch MMU on after the MMU is
 	 * switched to host, to avoid the P9_RADIX_PREFETCH_BUG.
 	 */
+	if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) &&
+	    vcpu->arch.shregs.msr & MSR_TS_MASK)
+		msr |= MSR_TS_S;
+
 	__mtmsrd(msr, 0);
 
 	end_timing(vcpu);