powerpc/kvm/book3s_hv: Preserve guest CFAR register value

The CFAR (Come-From Address Register) is a useful debugging aid that
exists on POWER7 processors.  Currently HV KVM doesn't save or restore
the CFAR register for guest vcpus, making the CFAR of limited use in
guests.

This adds the necessary code to capture the CFAR value saved in the
early exception entry code (it has to be saved before any branch is
executed), save it in the vcpu.arch struct, and restore it on entry
to the guest.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/exception-64s.h

@@ -199,10 +199,14 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 
 #define __KVM_HANDLER(area, h, n)					\
 do_kvm_##n:								\
+	BEGIN_FTR_SECTION_NESTED(947)					\
+	ld	r10,area+EX_CFAR(r13);					\
+	std	r10,HSTATE_CFAR(r13);					\
+	END_FTR_SECTION_NESTED(CPU_FTR_CFAR,CPU_FTR_CFAR,947);		\
 	ld	r10,area+EX_R10(r13);					\
-	stw	r9,HSTATE_SCRATCH1(r13);			\
+	stw	r9,HSTATE_SCRATCH1(r13);				\
 	ld	r9,area+EX_R9(r13);					\
-	std	r12,HSTATE_SCRATCH0(r13);			\
+	std	r12,HSTATE_SCRATCH0(r13);				\
 	li	r12,n;							\
 	b	kvmppc_interrupt
 

arch/powerpc/include/asm/kvm_book3s_asm.h

@@ -93,6 +93,9 @@ struct kvmppc_host_state {
 	u64 host_dscr;
 	u64 dec_expires;
 #endif
+#ifdef CONFIG_PPC_BOOK3S_64
+	u64 cfar;
+#endif
 };
 
 struct kvmppc_book3s_shadow_vcpu {

arch/powerpc/include/asm/kvm_host.h

@@ -440,6 +440,7 @@ struct kvm_vcpu_arch {
 	ulong uamor;
 	u32 ctrl;
 	ulong dabr;
+	ulong cfar;
 #endif
 	u32 vrsave; /* also USPRG0 */
 	u32 mmucr;

arch/powerpc/kernel/asm-offsets.c

@@ -479,6 +479,7 @@ int main(void)
 	DEFINE(VCPU_LAST_INST, offsetof(struct kvm_vcpu, arch.last_inst));
 	DEFINE(VCPU_TRAP, offsetof(struct kvm_vcpu, arch.trap));
 	DEFINE(VCPU_PTID, offsetof(struct kvm_vcpu, arch.ptid));
+	DEFINE(VCPU_CFAR, offsetof(struct kvm_vcpu, arch.cfar));
 	DEFINE(VCORE_ENTRY_EXIT, offsetof(struct kvmppc_vcore, entry_exit_count));
 	DEFINE(VCORE_NAP_COUNT, offsetof(struct kvmppc_vcore, nap_count));
 	DEFINE(VCORE_IN_GUEST, offsetof(struct kvmppc_vcore, in_guest));
@@ -558,6 +559,10 @@ int main(void)
 	DEFINE(IPI_PRIORITY, IPI_PRIORITY);
 #endif /* CONFIG_KVM_BOOK3S_64_HV */
 
+#ifdef CONFIG_PPC_BOOK3S_64
+	HSTATE_FIELD(HSTATE_CFAR, cfar);
+#endif /* CONFIG_PPC_BOOK3S_64 */
+
 #else /* CONFIG_PPC_BOOK3S */
 	DEFINE(VCPU_CR, offsetof(struct kvm_vcpu, arch.cr));
 	DEFINE(VCPU_XER, offsetof(struct kvm_vcpu, arch.xer));

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -539,6 +539,11 @@ fast_guest_return:
 
 	/* Enter guest */
 
+BEGIN_FTR_SECTION
+	ld	r5, VCPU_CFAR(r4)
+	mtspr	SPRN_CFAR, r5
+END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
+
 	ld	r5, VCPU_LR(r4)
 	lwz	r6, VCPU_CR(r4)
 	mtlr	r5
@@ -604,6 +609,10 @@ kvmppc_interrupt:
 	lwz	r4, HSTATE_SCRATCH1(r13)
 	std	r3, VCPU_GPR(R12)(r9)
 	stw	r4, VCPU_CR(r9)
+BEGIN_FTR_SECTION
+	ld	r3, HSTATE_CFAR(r13)
+	std	r3, VCPU_CFAR(r9)
+END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
 
 	/* Restore R1/R2 so we can handle faults */
 	ld	r1, HSTATE_HOST_R1(r13)