KVM: PPC: Book3S HV: Save/restore XER in checkpointed register state

When switching from/to a guest that has a transaction in progress,
we need to save/restore the checkpointed register state.  Although
XER is part of the CPU state that gets checkpointed, the code that
does this saving and restoring doesn't save/restore XER.

This fixes it by saving and restoring the XER.  To allow userspace
to read/write the checkpointed XER value, we also add a new ONE_REG
specifier.

The visible effect of this bug is that the guest may see its XER
value being corrupted when it uses transactions.

Fixes: e4e38121507a ("KVM: PPC: Book3S HV: Add transactional memory support")
Fixes: 0a8eccefcb34 ("KVM: PPC: Book3S HV: Add missing code for transaction reclaim on guest exit")
Cc: stable@vger.kernel.org # v3.15+
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

Documentation/virtual/kvm/api.txt

@@ -2039,6 +2039,7 @@ registers, find a list below:
   PPC   | KVM_REG_PPC_TM_VSCR           | 32
   PPC   | KVM_REG_PPC_TM_DSCR           | 64
   PPC   | KVM_REG_PPC_TM_TAR            | 64
+  PPC   | KVM_REG_PPC_TM_XER            | 64
         |                               |
   MIPS  | KVM_REG_MIPS_R0               | 64
           ...

arch/powerpc/include/asm/kvm_host.h

@@ -565,6 +565,7 @@ struct kvm_vcpu_arch {
 	u64 tfiar;
 
 	u32 cr_tm;
+	u64 xer_tm;
 	u64 lr_tm;
 	u64 ctr_tm;
 	u64 amr_tm;

arch/powerpc/include/uapi/asm/kvm.h

@@ -596,6 +596,7 @@ struct kvm_get_htab_header {
 #define KVM_REG_PPC_TM_VSCR	(KVM_REG_PPC_TM | KVM_REG_SIZE_U32 | 0x67)
 #define KVM_REG_PPC_TM_DSCR	(KVM_REG_PPC_TM | KVM_REG_SIZE_U64 | 0x68)
 #define KVM_REG_PPC_TM_TAR	(KVM_REG_PPC_TM | KVM_REG_SIZE_U64 | 0x69)
+#define KVM_REG_PPC_TM_XER	(KVM_REG_PPC_TM | KVM_REG_SIZE_U64 | 0x6a)
 
 /* PPC64 eXternal Interrupt Controller Specification */
 #define KVM_DEV_XICS_GRP_SOURCES	1	/* 64-bit source attributes */

arch/powerpc/kernel/asm-offsets.c

@@ -569,6 +569,7 @@ int main(void)
 	DEFINE(VCPU_VRS_TM, offsetof(struct kvm_vcpu, arch.vr_tm.vr));
 	DEFINE(VCPU_VRSAVE_TM, offsetof(struct kvm_vcpu, arch.vrsave_tm));
 	DEFINE(VCPU_CR_TM, offsetof(struct kvm_vcpu, arch.cr_tm));
+	DEFINE(VCPU_XER_TM, offsetof(struct kvm_vcpu, arch.xer_tm));
 	DEFINE(VCPU_LR_TM, offsetof(struct kvm_vcpu, arch.lr_tm));
 	DEFINE(VCPU_CTR_TM, offsetof(struct kvm_vcpu, arch.ctr_tm));
 	DEFINE(VCPU_AMR_TM, offsetof(struct kvm_vcpu, arch.amr_tm));

arch/powerpc/kvm/book3s_hv.c

@@ -1288,6 +1288,9 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 	case KVM_REG_PPC_TM_CR:
 		*val = get_reg_val(id, vcpu->arch.cr_tm);
 		break;
+	case KVM_REG_PPC_TM_XER:
+		*val = get_reg_val(id, vcpu->arch.xer_tm);
+		break;
 	case KVM_REG_PPC_TM_LR:
 		*val = get_reg_val(id, vcpu->arch.lr_tm);
 		break;
@@ -1498,6 +1501,9 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 	case KVM_REG_PPC_TM_CR:
 		vcpu->arch.cr_tm = set_reg_val(id, *val);
 		break;
+	case KVM_REG_PPC_TM_XER:
+		vcpu->arch.xer_tm = set_reg_val(id, *val);
+		break;
 	case KVM_REG_PPC_TM_LR:
 		vcpu->arch.lr_tm = set_reg_val(id, *val);
 		break;

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -2600,11 +2600,13 @@ kvmppc_save_tm:
 	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)
@@ -2697,11 +2699,13 @@ kvmppc_restore_tm:
 	ld	r7, VCPU_CTR_TM(r4)
 	ld	r8, VCPU_AMR_TM(r4)
 	ld	r9, VCPU_TAR_TM(r4)
+	ld	r10, VCPU_XER_TM(r4)
 	mtlr	r5
 	mtcr	r6
 	mtctr	r7
 	mtspr	SPRN_AMR, r8
 	mtspr	SPRN_TAR, r9
+	mtxer	r10
 
 	/*
 	 * Load up PPR and DSCR values but don't put them in the actual SPRs