KVM: PPC: Book3S: Rework TM save/restore code and make it C-callable

This adds a parameter to __kvmppc_save_tm and __kvmppc_restore_tm
which allows the caller to indicate whether it wants the nonvolatile
register state to be preserved across the call, as required by the C
calling conventions.  This parameter being non-zero also causes the
MSR bits that enable TM, FP, VMX and VSX to be preserved.  The
condition register and DSCR are now always preserved.

With this, kvmppc_save_tm_hv and kvmppc_restore_tm_hv can be called
from C code provided the 3rd parameter is non-zero.  So that these
functions can be called from modules, they now include code to set
the TOC pointer (r2) on entry, as they can call other built-in C
functions which will assume the TOC to have been set.

Also, the fake suspend code in kvmppc_save_tm_hv is modified here to
assume that treclaim in fake-suspend state does not modify any registers,
which is the case on POWER9.  This enables the code to be simplified
quite a bit.

_kvmppc_save_tm_pr and _kvmppc_restore_tm_pr become much simpler with
this change, since they now only need to save and restore TAR and pass
1 for the 3rd argument to __kvmppc_{save,restore}_tm.
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NPaul Mackerras <paulus@ozlabs.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/asm-prototypes.h

@@ -150,6 +150,16 @@ extern s32 patch__memset_nocache, patch__memcpy_nocache;
 
 extern long flush_count_cache;
 
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+void kvmppc_save_tm_hv(struct kvm_vcpu *vcpu, u64 msr, bool preserve_nv);
+void kvmppc_restore_tm_hv(struct kvm_vcpu *vcpu, u64 msr, bool preserve_nv);
+#else
+static inline void kvmppc_save_tm_hv(struct kvm_vcpu *vcpu, u64 msr,
+				     bool preserve_nv) { }
+static inline void kvmppc_restore_tm_hv(struct kvm_vcpu *vcpu, u64 msr,
+					bool preserve_nv) { }
+#endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
+
 void kvmhv_save_host_pmu(void);
 void kvmhv_load_host_pmu(void);
 void kvmhv_save_guest_pmu(struct kvm_vcpu *vcpu, bool pmu_in_use);

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -759,11 +759,13 @@ BEGIN_FTR_SECTION
 	b	91f
 END_FTR_SECTION(CPU_FTR_TM | CPU_FTR_P9_TM_HV_ASSIST, 0)
 	/*
-	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS (but not CR)
 	 */
 	mr      r3, r4
 	ld      r4, VCPU_MSR(r3)
+	li	r5, 0			/* don't preserve non-vol regs */
 	bl	kvmppc_restore_tm_hv
+	nop
 	ld	r4, HSTATE_KVM_VCPU(r13)
 91:
 #endif
@@ -1603,11 +1605,13 @@ BEGIN_FTR_SECTION
 	b	91f
 END_FTR_SECTION(CPU_FTR_TM | CPU_FTR_P9_TM_HV_ASSIST, 0)
 	/*
-	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS (but not CR)
 	 */
 	mr      r3, r9
 	ld      r4, VCPU_MSR(r3)
+	li	r5, 0			/* don't preserve non-vol regs */
 	bl	kvmppc_save_tm_hv
+	nop
 	ld	r9, HSTATE_KVM_VCPU(r13)
 91:
 #endif
@@ -2486,11 +2490,13 @@ BEGIN_FTR_SECTION
 	b	91f
 END_FTR_SECTION(CPU_FTR_TM | CPU_FTR_P9_TM_HV_ASSIST, 0)
 	/*
-	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS (but not CR)
 	 */
 	ld	r3, HSTATE_KVM_VCPU(r13)
 	ld      r4, VCPU_MSR(r3)
+	li	r5, 0			/* don't preserve non-vol regs */
 	bl	kvmppc_save_tm_hv
+	nop
 91:
 #endif
 
@@ -2606,11 +2612,13 @@ BEGIN_FTR_SECTION
 	b	91f
 END_FTR_SECTION(CPU_FTR_TM | CPU_FTR_P9_TM_HV_ASSIST, 0)
 	/*
-	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+	 * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS (but not CR)
 	 */
 	mr      r3, r4
 	ld      r4, VCPU_MSR(r3)
+	li	r5, 0			/* don't preserve non-vol regs */
 	bl	kvmppc_restore_tm_hv
+	nop
 	ld	r4, HSTATE_KVM_VCPU(r13)
 91:
 #endif
@@ -2943,10 +2951,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
  * Save transactional state and TM-related registers.
  * Called with r3 pointing to the vcpu struct and r4 containing
  * the guest MSR value.
- * This can modify all checkpointed registers, but
+ * r5 is non-zero iff non-volatile register state needs to be maintained.
+ * If r5 == 0, this can modify all checkpointed registers, but
  * restores r1 and r2 before exit.
  */
-kvmppc_save_tm_hv:
+_GLOBAL_TOC(kvmppc_save_tm_hv)
+EXPORT_SYMBOL_GPL(kvmppc_save_tm_hv)
 	/* See if we need to handle fake suspend mode */
 BEGIN_FTR_SECTION
 	b	__kvmppc_save_tm
@@ -2974,12 +2984,6 @@ BEGIN_FTR_SECTION
 END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_XER_SO_BUG)
 	nop
 
-	std	r1, HSTATE_HOST_R1(r13)
-
-	/* Clear the MSR RI since r1, r13 may be foobar. */
-	li	r5, 0
-	mtmsrd	r5, 1
-
 	/* We have to treclaim here because that's the only way to do S->N */
 	li	r3, TM_CAUSE_KVM_RESCHED
 	TRECLAIM(R3)
@@ -2988,22 +2992,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_XER_SO_BUG)
 	 * We were in fake suspend, so we are not going to save the
 	 * register state as the guest checkpointed state (since
 	 * we already have it), therefore we can now use any volatile GPR.
+	 * In fact treclaim in fake suspend state doesn't modify
+	 * any registers.
 	 */
-	/* Reload PACA pointer, stack pointer and TOC. */
-	GET_PACA(r13)
-	ld	r1, HSTATE_HOST_R1(r13)
-	ld	r2, PACATOC(r13)
 
-	/* Set MSR RI now we have r1 and r13 back. */
-	li	r5, MSR_RI
-	mtmsrd	r5, 1
-
-	HMT_MEDIUM
-	ld	r6, HSTATE_DSCR(r13)
-	mtspr	SPRN_DSCR, r6
-BEGIN_FTR_SECTION_NESTED(96)
+BEGIN_FTR_SECTION
 	bl	pnv_power9_force_smt4_release
-END_FTR_SECTION_NESTED(CPU_FTR_P9_TM_XER_SO_BUG, CPU_FTR_P9_TM_XER_SO_BUG, 96)
+END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_XER_SO_BUG)
 	nop
 
 4:
@@ -3029,10 +3024,12 @@ END_FTR_SECTION_NESTED(CPU_FTR_P9_TM_XER_SO_BUG, CPU_FTR_P9_TM_XER_SO_BUG, 96)
  * Restore transactional state and TM-related registers.
  * Called with r3 pointing to the vcpu struct
  * and r4 containing the guest MSR value.
+ * r5 is non-zero iff non-volatile register state needs to be maintained.
  * This potentially modifies all checkpointed registers.
  * It restores r1 and r2 from the PACA.
  */
-kvmppc_restore_tm_hv:
+_GLOBAL_TOC(kvmppc_restore_tm_hv)
+EXPORT_SYMBOL_GPL(kvmppc_restore_tm_hv)
 	/*
 	 * If we are doing TM emulation for the guest on a POWER9 DD2,
 	 * then we don't actually do a trechkpt -- we either set up

arch/powerpc/kvm/tm.S

@@ -28,17 +28,25 @@
  * Save transactional state and TM-related registers.
  * Called with:
  * - r3 pointing to the vcpu struct
- * - r4 points to the MSR with current TS bits:
+ * - r4 containing the MSR with current TS bits:
  * 	(For HV KVM, it is VCPU_MSR ; For PR KVM, it is host MSR).
- * This can modify all checkpointed registers, but
- * restores r1, r2 before exit.
+ * - r5 containing a flag indicating that non-volatile registers
+ *	must be preserved.
+ * If r5 == 0, this can modify all checkpointed registers, but
+ * restores r1, r2 before exit.  If r5 != 0, this restores the
+ * MSR TM/FP/VEC/VSX bits to their state on entry.
  */
 _GLOBAL(__kvmppc_save_tm)
 	mflr	r0
 	std	r0, PPC_LR_STKOFF(r1)
+	stdu    r1, -SWITCH_FRAME_SIZE(r1)
+
+	mr	r9, r3
+	cmpdi	cr7, r5, 0
 
 	/* Turn on TM. */
 	mfmsr	r8
+	mr	r10, r8
 	li	r0, 1
 	rldimi	r8, r0, MSR_TM_LG, 63-MSR_TM_LG
 	ori     r8, r8, MSR_FP
@@ -51,6 +59,27 @@ _GLOBAL(__kvmppc_save_tm)
 	std	r1, HSTATE_SCRATCH2(r13)
 	std	r3, HSTATE_SCRATCH1(r13)
 
+	/* Save CR on the stack - even if r5 == 0 we need to get cr7 back. */
+	mfcr	r6
+	SAVE_GPR(6, r1)
+
+	/* Save DSCR so we can restore it to avoid running with user value */
+	mfspr	r7, SPRN_DSCR
+	SAVE_GPR(7, r1)
+
+	/*
+	 * We are going to do treclaim., which will modify all checkpointed
+	 * registers.  Save the non-volatile registers on the stack if
+	 * preservation of non-volatile state has been requested.
+	 */
+	beq	cr7, 3f
+	SAVE_NVGPRS(r1)
+
+	/* MSR[TS] will be 0 (non-transactional) once we do treclaim. */
+	li	r0, 0
+	rldimi	r10, r0, MSR_TS_S_LG, 63 - MSR_TS_T_LG
+	SAVE_GPR(10, r1)	/* final MSR value */
+3:
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 BEGIN_FTR_SECTION
 	/* Emulation of the treclaim instruction needs TEXASR before treclaim */
@@ -74,22 +103,25 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
 	std	r9, PACATMSCRATCH(r13)
 	ld	r9, HSTATE_SCRATCH1(r13)
 
-	/* Get a few more GPRs free. */
-	std	r29, VCPU_GPRS_TM(29)(r9)
-	std	r30, VCPU_GPRS_TM(30)(r9)
-	std	r31, VCPU_GPRS_TM(31)(r9)
-
-	/* Save away PPR and DSCR soon so don't run with user values. */
-	mfspr	r31, SPRN_PPR
+	/* Save away PPR soon so we don't run with user value. */
+	std	r0, VCPU_GPRS_TM(0)(r9)
+	mfspr	r0, SPRN_PPR
 	HMT_MEDIUM
-	mfspr	r30, SPRN_DSCR
-#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
-	ld	r29, HSTATE_DSCR(r13)
-	mtspr	SPRN_DSCR, r29
-#endif
 
-	/* Save all but r9, r13 & r29-r31 */
-	reg = 0
+	/* Reload stack pointer. */
+	std	r1, VCPU_GPRS_TM(1)(r9)
+	ld	r1, HSTATE_SCRATCH2(r13)
+
+	/* Set MSR RI now we have r1 and r13 back. */
+	std	r2, VCPU_GPRS_TM(2)(r9)
+	li	r2, MSR_RI
+	mtmsrd	r2, 1
+
+	/* Reload TOC pointer. */
+	ld	r2, PACATOC(r13)
+
+	/* Save all but r0-r2, r9 & r13 */
+	reg = 3
 	.rept	29
 	.if (reg != 9) && (reg != 13)
 	std	reg, VCPU_GPRS_TM(reg)(r9)
@@ -103,33 +135,29 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
 	ld	r4, PACATMSCRATCH(r13)
 	std	r4, VCPU_GPRS_TM(9)(r9)
 
-	/* Reload stack pointer and TOC. */
-	ld	r1, HSTATE_SCRATCH2(r13)
-	ld	r2, PACATOC(r13)
-
-	/* Set MSR RI now we have r1 and r13 back. */
-	li	r5, MSR_RI
-	mtmsrd	r5, 1
+	/* Restore host DSCR and CR values, after saving guest values */
+	mfcr	r6
+	mfspr	r7, SPRN_DSCR
+	stw	r6, VCPU_CR_TM(r9)
+	std	r7, VCPU_DSCR_TM(r9)
+	REST_GPR(6, r1)
+	REST_GPR(7, r1)
+	mtcr	r6
+	mtspr	SPRN_DSCR, r7
 
-	/* Save away checkpinted SPRs. */
-	std	r31, VCPU_PPR_TM(r9)
-	std	r30, VCPU_DSCR_TM(r9)
+	/* Save away checkpointed SPRs. */
+	std	r0, VCPU_PPR_TM(r9)
 	mflr	r5
-	mfcr	r6
 	mfctr	r7
 	mfspr	r8, SPRN_AMR
 	mfspr	r10, SPRN_TAR
 	mfxer	r11
 	std	r5, VCPU_LR_TM(r9)
-	stw	r6, VCPU_CR_TM(r9)
 	std	r7, VCPU_CTR_TM(r9)
 	std	r8, VCPU_AMR_TM(r9)
 	std	r10, VCPU_TAR_TM(r9)
 	std	r11, VCPU_XER_TM(r9)
 
-	/* Restore r12 as trap number. */
-	lwz	r12, VCPU_TRAP(r9)
-
 	/* Save FP/VSX. */
 	addi	r3, r9, VCPU_FPRS_TM
 	bl	store_fp_state
@@ -137,6 +165,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
 	bl	store_vr_state
 	mfspr	r6, SPRN_VRSAVE
 	stw	r6, VCPU_VRSAVE_TM(r9)
+
+	/* Restore non-volatile registers if requested to */
+	beq	cr7, 1f
+	REST_NVGPRS(r1)
+	REST_GPR(10, r1)
 1:
 	/*
 	 * We need to save these SPRs after the treclaim so that the software
@@ -146,12 +179,16 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
 	 */
 	mfspr	r7, SPRN_TEXASR
 	std	r7, VCPU_TEXASR(r9)
-11:
 	mfspr	r5, SPRN_TFHAR
 	mfspr	r6, SPRN_TFIAR
 	std	r5, VCPU_TFHAR(r9)
 	std	r6, VCPU_TFIAR(r9)
 
+	/* Restore MSR state if requested */
+	beq	cr7, 2f
+	mtmsrd	r10, 0
+2:
+	addi	r1, r1, SWITCH_FRAME_SIZE
 	ld	r0, PPC_LR_STKOFF(r1)
 	mtlr	r0
 	blr
@@ -161,49 +198,22 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
  * be invoked from C function by PR KVM only.
  */
 _GLOBAL(_kvmppc_save_tm_pr)
-	mflr	r5
-	std	r5, PPC_LR_STKOFF(r1)
-	stdu    r1, -SWITCH_FRAME_SIZE(r1)
-	SAVE_NVGPRS(r1)
-
-	/* save MSR since TM/math bits might be impacted
-	 * by __kvmppc_save_tm().
-	 */
-	mfmsr	r5
-	SAVE_GPR(5, r1)
-
-	/* also save DSCR/CR/TAR so that it can be recovered later */
-	mfspr   r6, SPRN_DSCR
-	SAVE_GPR(6, r1)
-
-	mfcr    r7
-	stw     r7, _CCR(r1)
+	mflr	r0
+	std	r0, PPC_LR_STKOFF(r1)
+	stdu    r1, -PPC_MIN_STKFRM(r1)
 
 	mfspr   r8, SPRN_TAR
-	SAVE_GPR(8, r1)
+	std	r8, PPC_MIN_STKFRM-8(r1)
 
+	li	r5, 1		/* preserve non-volatile registers */
 	bl	__kvmppc_save_tm
 
-	REST_GPR(8, r1)
+	ld	r8, PPC_MIN_STKFRM-8(r1)
 	mtspr   SPRN_TAR, r8
 
-	ld      r7, _CCR(r1)
-	mtcr	r7
-
-	REST_GPR(6, r1)
-	mtspr   SPRN_DSCR, r6
-
-	/* need preserve current MSR's MSR_TS bits */
-	REST_GPR(5, r1)
-	mfmsr   r6
-	rldicl  r6, r6, 64 - MSR_TS_S_LG, 62
-	rldimi  r5, r6, MSR_TS_S_LG, 63 - MSR_TS_T_LG
-	mtmsrd  r5
-
-	REST_NVGPRS(r1)
-	addi    r1, r1, SWITCH_FRAME_SIZE
-	ld	r5, PPC_LR_STKOFF(r1)
-	mtlr	r5
+	addi    r1, r1, PPC_MIN_STKFRM
+	ld	r0, PPC_LR_STKOFF(r1)
+	mtlr	r0
 	blr
 
 EXPORT_SYMBOL_GPL(_kvmppc_save_tm_pr);
@@ -215,15 +225,21 @@ EXPORT_SYMBOL_GPL(_kvmppc_save_tm_pr);
  *  - r4 is the guest MSR with desired TS bits:
  * 	For HV KVM, it is VCPU_MSR
  * 	For PR KVM, it is provided by caller
- * This potentially modifies all checkpointed registers.
- * It restores r1, r2 from the PACA.
+ * - r5 containing a flag indicating that non-volatile registers
+ *	must be preserved.
+ * If r5 == 0, this potentially modifies all checkpointed registers, but
+ * restores r1, r2 from the PACA before exit.
+ * If r5 != 0, this restores the MSR TM/FP/VEC/VSX bits to their state on entry.
  */
 _GLOBAL(__kvmppc_restore_tm)
 	mflr	r0
 	std	r0, PPC_LR_STKOFF(r1)
 
+	cmpdi	cr7, r5, 0
+
 	/* Turn on TM/FP/VSX/VMX so we can restore them. */
 	mfmsr	r5
+	mr	r10, r5
 	li	r6, MSR_TM >> 32
 	sldi	r6, r6, 32
 	or	r5, r5, r6
@@ -244,8 +260,7 @@ _GLOBAL(__kvmppc_restore_tm)
 
 	mr	r5, r4
 	rldicl. r5, r5, 64 - MSR_TS_S_LG, 62
-	beqlr		/* TM not active in guest */
-	std	r1, HSTATE_SCRATCH2(r13)
+	beq	9f		/* TM not active in guest */
 
 	/* Make sure the failure summary is set, otherwise we'll program check
 	 * when we trechkpt.  It's possible that this might have been not set
@@ -255,6 +270,26 @@ _GLOBAL(__kvmppc_restore_tm)
 	oris	r7, r7, (TEXASR_FS)@h
 	mtspr	SPRN_TEXASR, r7
 
+	/*
+	 * Make a stack frame and save non-volatile registers if requested.
+	 */
+	stdu	r1, -SWITCH_FRAME_SIZE(r1)
+	std	r1, HSTATE_SCRATCH2(r13)
+
+	mfcr	r6
+	mfspr	r7, SPRN_DSCR
+	SAVE_GPR(2, r1)
+	SAVE_GPR(6, r1)
+	SAVE_GPR(7, r1)
+
+	beq	cr7, 4f
+	SAVE_NVGPRS(r1)
+
+	/* MSR[TS] will be 1 (suspended) once we do trechkpt */
+	li	r0, 1
+	rldimi	r10, r0, MSR_TS_S_LG, 63 - MSR_TS_T_LG
+	SAVE_GPR(10, r1)	/* final MSR value */
+4:
 	/*
 	 * We need to load up the checkpointed state for the guest.
 	 * We need to do this early as it will blow away any GPRs, VSRs and
@@ -291,8 +326,6 @@ _GLOBAL(__kvmppc_restore_tm)
 	ld	r29, VCPU_DSCR_TM(r3)
 	ld	r30, VCPU_PPR_TM(r3)
 
-	std	r2, PACATMSCRATCH(r13) /* Save TOC */
-
 	/* Clear the MSR RI since r1, r13 are all going to be foobar. */
 	li	r5, 0
 	mtmsrd	r5, 1
@@ -318,18 +351,31 @@ _GLOBAL(__kvmppc_restore_tm)
 	/* Now let's get back the state we need. */
 	HMT_MEDIUM
 	GET_PACA(r13)
-#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
-	ld	r29, HSTATE_DSCR(r13)
-	mtspr	SPRN_DSCR, r29
-#endif
 	ld	r1, HSTATE_SCRATCH2(r13)
-	ld	r2, PACATMSCRATCH(r13)
+	REST_GPR(7, r1)
+	mtspr	SPRN_DSCR, r7
 
 	/* Set the MSR RI since we have our registers back. */
 	li	r5, MSR_RI
 	mtmsrd	r5, 1
+
+	/* Restore TOC pointer and CR */
+	REST_GPR(2, r1)
+	REST_GPR(6, r1)
+	mtcr	r6
+
+	/* Restore non-volatile registers if requested to. */
+	beq	cr7, 5f
+	REST_GPR(10, r1)
+	REST_NVGPRS(r1)
+
+5:	addi	r1, r1, SWITCH_FRAME_SIZE
 	ld	r0, PPC_LR_STKOFF(r1)
 	mtlr	r0
+
+9:	/* Restore MSR bits if requested */
+	beqlr	cr7
+	mtmsrd	r10, 0
 	blr
 
 /*
@@ -337,47 +383,23 @@ _GLOBAL(__kvmppc_restore_tm)
  * can be invoked from C function by PR KVM only.
  */
 _GLOBAL(_kvmppc_restore_tm_pr)
-	mflr	r5
-	std	r5, PPC_LR_STKOFF(r1)
-	stdu    r1, -SWITCH_FRAME_SIZE(r1)
-	SAVE_NVGPRS(r1)
-
-	/* save MSR to avoid TM/math bits change */
-	mfmsr	r5
-	SAVE_GPR(5, r1)
-
-	/* also save DSCR/CR/TAR so that it can be recovered later */
-	mfspr   r6, SPRN_DSCR
-	SAVE_GPR(6, r1)
-
-	mfcr    r7
-	stw     r7, _CCR(r1)
+	mflr	r0
+	std	r0, PPC_LR_STKOFF(r1)
+	stdu    r1, -PPC_MIN_STKFRM(r1)
 
+	/* save TAR so that it can be recovered later */
 	mfspr   r8, SPRN_TAR
-	SAVE_GPR(8, r1)
+	std	r8, PPC_MIN_STKFRM-8(r1)
 
+	li	r5, 1
 	bl	__kvmppc_restore_tm
 
-	REST_GPR(8, r1)
+	ld	r8, PPC_MIN_STKFRM-8(r1)
 	mtspr   SPRN_TAR, r8
 
-	ld      r7, _CCR(r1)
-	mtcr	r7
-
-	REST_GPR(6, r1)
-	mtspr   SPRN_DSCR, r6
-
-	/* need preserve current MSR's MSR_TS bits */
-	REST_GPR(5, r1)
-	mfmsr   r6
-	rldicl  r6, r6, 64 - MSR_TS_S_LG, 62
-	rldimi  r5, r6, MSR_TS_S_LG, 63 - MSR_TS_T_LG
-	mtmsrd  r5
-
-	REST_NVGPRS(r1)
-	addi    r1, r1, SWITCH_FRAME_SIZE
-	ld	r5, PPC_LR_STKOFF(r1)
-	mtlr	r5
+	addi    r1, r1, PPC_MIN_STKFRM
+	ld	r0, PPC_LR_STKOFF(r1)
+	mtlr	r0
 	blr
 
 EXPORT_SYMBOL_GPL(_kvmppc_restore_tm_pr);