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>

5 files changed, 24 insertions, 2 deletions

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 4dfc51588be5..05e6d2ee1db9 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/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
 
diff --git a/arch/powerpc/include/asm/kvm_book3s_asm.h b/arch/powerpc/include/asm/kvm_book3s_asm.h
index 88609b23b775..cdc3d2717cc6 100644
--- a/arch/powerpc/include/asm/kvm_book3s_asm.h
+++ b/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 {
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index ca9bf459db6a..03d7beae89a0 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/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;
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index beddba432518..e295a09b1f06 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/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));
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 10b6c358dd77..e33d11f1b977 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/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)