KVM: PPC: Book3S PR: Always fail transactions in guest privileged state

Currently the kernel doesn't use transaction memory.
And there is an issue for privileged state in the guest that:
tbegin/tsuspend/tresume/tabort TM instructions can impact MSR TM bits
without trapping into the PR host. So following code will lead to a
false mfmsr result:
	tbegin	<- MSR bits update to Transaction active.
	beq 	<- failover handler branch
	mfmsr	<- still read MSR bits from magic page with
		transaction inactive.

It is not an issue for non-privileged guest state since its mfmsr is
not patched with magic page and will always trap into the PR host.

This patch will always fail tbegin attempt for privileged state in the
guest, so that the above issue is prevented. It is benign since
currently (guest) kernel doesn't initiate a transaction.

Test case:
https://github.com/justdoitqd/publicFiles/blob/master/test_tbegin_pr.c

Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/include/asm/kvm_book3s.h

@@ -262,9 +262,11 @@ extern void kvmppc_copy_from_svcpu(struct kvm_vcpu *vcpu);
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 void kvmppc_save_tm_pr(struct kvm_vcpu *vcpu);
 void kvmppc_restore_tm_pr(struct kvm_vcpu *vcpu);
+void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu);
 #else
 static inline void kvmppc_save_tm_pr(struct kvm_vcpu *vcpu) {}
 static inline void kvmppc_restore_tm_pr(struct kvm_vcpu *vcpu) {}
+static inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu) {}
 #endif
 
 extern int kvm_irq_bypass;

arch/powerpc/kvm/book3s_emulate.c

@@ -23,6 +23,7 @@
 #include <asm/reg.h>
 #include <asm/switch_to.h>
 #include <asm/time.h>
+#include <asm/tm.h>
 #include "book3s.h"
 #include <asm/asm-prototypes.h>
 
@@ -48,6 +49,8 @@
 #define OP_31_XOP_EIOIO		854
 #define OP_31_XOP_SLBMFEE	915
 
+#define OP_31_XOP_TBEGIN	654
+
 /* DCBZ is actually 1014, but we patch it to 1010 so we get a trap */
 #define OP_31_XOP_DCBZ		1010
 
@@ -363,6 +366,43 @@ int kvmppc_core_emulate_op_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
 
 			break;
 		}
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+		case OP_31_XOP_TBEGIN:
+		{
+			if (!cpu_has_feature(CPU_FTR_TM))
+				break;
+
+			if (!(kvmppc_get_msr(vcpu) & MSR_TM)) {
+				kvmppc_trigger_fac_interrupt(vcpu, FSCR_TM_LG);
+				emulated = EMULATE_AGAIN;
+				break;
+			}
+
+			if (!(kvmppc_get_msr(vcpu) & MSR_PR)) {
+				preempt_disable();
+				vcpu->arch.cr = (CR0_TBEGIN_FAILURE |
+				  (vcpu->arch.cr & ~(CR0_MASK << CR0_SHIFT)));
+
+				vcpu->arch.texasr = (TEXASR_FS | TEXASR_EXACT |
+					(((u64)(TM_CAUSE_EMULATE | TM_CAUSE_PERSISTENT))
+						 << TEXASR_FC_LG));
+
+				if ((inst >> 21) & 0x1)
+					vcpu->arch.texasr |= TEXASR_ROT;
+
+				if (kvmppc_get_msr(vcpu) & MSR_HV)
+					vcpu->arch.texasr |= TEXASR_HV;
+
+				vcpu->arch.tfhar = kvmppc_get_pc(vcpu) + 4;
+				vcpu->arch.tfiar = kvmppc_get_pc(vcpu);
+
+				kvmppc_restore_tm_sprs(vcpu);
+				preempt_enable();
+			} else
+				emulated = EMULATE_FAIL;
+			break;
+		}
+#endif
 		default:
 			emulated = EMULATE_FAIL;
 		}

arch/powerpc/kvm/book3s_pr.c

@@ -206,6 +206,15 @@ static void kvmppc_recalc_shadow_msr(struct kvm_vcpu *vcpu)
 	/* 64-bit Process MSR values */
 #ifdef CONFIG_PPC_BOOK3S_64
 	smsr |= MSR_ISF | MSR_HV;
+#endif
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	/*
+	 * in guest privileged state, we want to fail all TM transactions.
+	 * So disable MSR TM bit so that all tbegin. will be able to be
+	 * trapped into host.
+	 */
+	if (!(guest_msr & MSR_PR))
+		smsr &= ~MSR_TM;
 #endif
 	vcpu->arch.shadow_msr = smsr;
 }
@@ -299,7 +308,7 @@ static inline void kvmppc_save_tm_sprs(struct kvm_vcpu *vcpu)
 	tm_disable();
 }
 
-static inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu)
+void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu)
 {
 	tm_enable();
 	mtspr(SPRN_TFHAR, vcpu->arch.tfhar);