KVM: PPC: Book3S HV: Save/restore host values of debug registers

At present, HV KVM on POWER8 and POWER9 machines loses any instruction
or data breakpoint set in the host whenever a guest is run.
Instruction breakpoints are currently only used by xmon, but ptrace
and the perf_event subsystem can set data breakpoints as well as xmon.

To fix this, we save the host values of the debug registers (CIABR,
DAWR and DAWRX) before entering the guest and restore them on exit.
To provide space to save them in the stack frame, we expand the stack
frame allocated by kvmppc_hv_entry() from 112 to 144 bytes.

Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08)
Cc: stable@vger.kernel.org # v3.14+
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -44,6 +44,17 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
 #define NAPPING_CEDE	1
 #define NAPPING_NOVCPU	2
 
+/* Stack frame offsets for kvmppc_hv_entry */
+#define SFS			144
+#define STACK_SLOT_TRAP		(SFS-4)
+#define STACK_SLOT_TID		(SFS-16)
+#define STACK_SLOT_PSSCR	(SFS-24)
+#define STACK_SLOT_PID		(SFS-32)
+#define STACK_SLOT_IAMR		(SFS-40)
+#define STACK_SLOT_CIABR	(SFS-48)
+#define STACK_SLOT_DAWR		(SFS-56)
+#define STACK_SLOT_DAWRX	(SFS-64)
+
 /*
  * Call kvmppc_hv_entry in real mode.
  * Must be called with interrupts hard-disabled.
@@ -328,10 +339,10 @@ kvm_novcpu_exit:
 	bl	kvmhv_accumulate_time
 #endif
 13:	mr	r3, r12
-	stw	r12, 112-4(r1)
+	stw	r12, STACK_SLOT_TRAP(r1)
 	bl	kvmhv_commence_exit
 	nop
-	lwz	r12, 112-4(r1)
+	lwz	r12, STACK_SLOT_TRAP(r1)
 	b	kvmhv_switch_to_host
 
 /*
@@ -554,12 +565,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
  *                                                                            *
  *****************************************************************************/
 
-/* Stack frame offsets */
-#define STACK_SLOT_TID		(112-16)
-#define STACK_SLOT_PSSCR	(112-24)
-#define STACK_SLOT_PID		(112-32)
-#define STACK_SLOT_IAMR		(112-40)
-
 .global kvmppc_hv_entry
 kvmppc_hv_entry:
 
@@ -575,7 +580,7 @@ kvmppc_hv_entry:
 	 */
 	mflr	r0
 	std	r0, PPC_LR_STKOFF(r1)
-	stdu	r1, -112(r1)
+	stdu	r1, -SFS(r1)
 
 	/* Save R1 in the PACA */
 	std	r1, HSTATE_HOST_R1(r13)
@@ -765,6 +770,14 @@ BEGIN_FTR_SECTION
 	std	r7, STACK_SLOT_PID(r1)
 	std	r8, STACK_SLOT_IAMR(r1)
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
+BEGIN_FTR_SECTION
+	mfspr	r5, SPRN_CIABR
+	mfspr	r6, SPRN_DAWR
+	mfspr	r7, SPRN_DAWRX
+	std	r5, STACK_SLOT_CIABR(r1)
+	std	r6, STACK_SLOT_DAWR(r1)
+	std	r7, STACK_SLOT_DAWRX(r1)
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 
 BEGIN_FTR_SECTION
 	/* Set partition DABR */
@@ -1518,8 +1531,6 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
 	 * set by the guest could disrupt the host.
 	 */
 	li	r0, 0
-	mtspr	SPRN_CIABR, r0
-	mtspr	SPRN_DAWRX, r0
 	mtspr	SPRN_PSPB, r0
 	mtspr	SPRN_WORT, r0
 BEGIN_FTR_SECTION
@@ -1684,6 +1695,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	ptesync
 
 	/* Restore host values of some registers */
+BEGIN_FTR_SECTION
+	ld	r5, STACK_SLOT_CIABR(r1)
+	ld	r6, STACK_SLOT_DAWR(r1)
+	ld	r7, STACK_SLOT_DAWRX(r1)
+	mtspr	SPRN_CIABR, r5
+	mtspr	SPRN_DAWR, r6
+	mtspr	SPRN_DAWRX, r7
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 BEGIN_FTR_SECTION
 	ld	r5, STACK_SLOT_TID(r1)
 	ld	r6, STACK_SLOT_PSSCR(r1)
@@ -1836,8 +1855,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
 	li	r0, KVM_GUEST_MODE_NONE
 	stb	r0, HSTATE_IN_GUEST(r13)
 
-	ld	r0, 112+PPC_LR_STKOFF(r1)
-	addi	r1, r1, 112
+	ld	r0, SFS+PPC_LR_STKOFF(r1)
+	addi	r1, r1, SFS
 	mtlr	r0
 	blr