KVM: PPC: Book3S PR: Load up SPRG3 register with guest value on guest entry

Unlike the other general-purpose SPRs, SPRG3 can be read by usermode
code, and is used in recent kernels to store the CPU and NUMA node
numbers so that they can be read by VDSO functions.  Thus we need to
load the guest's SPRG3 value into the real SPRG3 register when entering
the guest, and restore the host's value when exiting the guest.  We don't
need to save the guest SPRG3 value when exiting the guest as usermode
code can't modify SPRG3.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kernel/asm-offsets.c

@@ -452,6 +452,7 @@ int main(void)
 	DEFINE(VCPU_SPRG2, offsetof(struct kvm_vcpu, arch.shregs.sprg2));
 	DEFINE(VCPU_SPRG3, offsetof(struct kvm_vcpu, arch.shregs.sprg3));
 #endif
+	DEFINE(VCPU_SHARED_SPRG3, offsetof(struct kvm_vcpu_arch_shared, sprg3));
 	DEFINE(VCPU_SHARED_SPRG4, offsetof(struct kvm_vcpu_arch_shared, sprg4));
 	DEFINE(VCPU_SHARED_SPRG5, offsetof(struct kvm_vcpu_arch_shared, sprg5));
 	DEFINE(VCPU_SHARED_SPRG6, offsetof(struct kvm_vcpu_arch_shared, sprg6));

arch/powerpc/kvm/book3s_interrupts.S

@@ -92,6 +92,11 @@ kvm_start_lightweight:
 	PPC_LL	r3, VCPU_HFLAGS(r4)
 	rldicl	r3, r3, 0, 63		/* r3 &= 1 */
 	stb	r3, HSTATE_RESTORE_HID5(r13)
+
+	/* Load up guest SPRG3 value, since it's user readable */
+	ld	r3, VCPU_SHARED(r4)
+	ld	r3, VCPU_SHARED_SPRG3(r3)
+	mtspr	SPRN_SPRG3, r3
 #endif /* CONFIG_PPC_BOOK3S_64 */
 
 	PPC_LL	r4, VCPU_SHADOW_MSR(r4)	/* get shadow_msr */
@@ -123,6 +128,15 @@ kvmppc_handler_highmem:
 	/* R7 = vcpu */
 	PPC_LL	r7, GPR4(r1)
 
+#ifdef CONFIG_PPC_BOOK3S_64
+	/*
+	 * Reload kernel SPRG3 value.
+	 * No need to save guest value as usermode can't modify SPRG3.
+	 */
+	ld	r3, PACA_SPRG3(r13)
+	mtspr	SPRN_SPRG3, r3
+#endif /* CONFIG_PPC_BOOK3S_64 */
+
 	PPC_STL	r14, VCPU_GPR(R14)(r7)
 	PPC_STL	r15, VCPU_GPR(R15)(r7)
 	PPC_STL	r16, VCPU_GPR(R16)(r7)