KVM: PPC: Call SLB patching code in interrupt safe manner

Currently we're racy when doing the transition from IR=1 to IR=0, from
the module memory entry code to the real mode SLB switching code.

To work around that I took a look at the RTAS entry code which is faced
with a similar problem and did the same thing:

  A small helper in linear mapped memory that does mtmsr with IR=0 and
  then RFIs info the actual handler.

Thanks to that trick we can safely take page faults in the entry code
and only need to be really wary of what to do as of the SLB switching
part.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

9 files changed, 34 insertions, 21 deletions

diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index f192017d799d..c91be0ff0232 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -121,6 +121,7 @@ extern void kvmppc_set_bat(struct kvm_vcpu *vcpu, struct kvmppc_bat *bat,
 
 extern u32 kvmppc_trampoline_lowmem;
 extern u32 kvmppc_trampoline_enter;
+extern void kvmppc_rmcall(ulong srr0, ulong srr1);
 
 static inline struct kvmppc_vcpu_book3s *to_book3s(struct kvm_vcpu *vcpu)
 {
diff --git a/arch/powerpc/include/asm/kvm_book3s_64_asm.h b/arch/powerpc/include/asm/kvm_book3s_64_asm.h
index fca9404c1a7d..183461b48407 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64_asm.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64_asm.h
@@ -69,7 +69,6 @@ struct kvmppc_book3s_shadow_vcpu {
 	ulong scratch0;
 	ulong scratch1;
 	ulong vmhandler;
-	ulong rmhandler;
 };
 
 #endif /*__ASSEMBLY__ */
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index d615fa8a1412..f7215e622dfd 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -167,6 +167,7 @@ struct kvm_vcpu_arch {
 	ulong trampoline_lowmem;
 	ulong trampoline_enter;
 	ulong highmem_handler;
+	ulong rmcall;
 	ulong host_paca_phys;
 	struct kvmppc_mmu mmu;
 #endif
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 1501e77c980c..ee9935442f0e 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -214,8 +214,6 @@ int main(void)
 	DEFINE(PACA_KVM_HOST_R2, offsetof(struct paca_struct, shadow_vcpu.host_r2));
 	DEFINE(PACA_KVM_VMHANDLER, offsetof(struct paca_struct,
 					    shadow_vcpu.vmhandler));
-	DEFINE(PACA_KVM_RMHANDLER, offsetof(struct paca_struct,
-					    shadow_vcpu.rmhandler));
 	DEFINE(PACA_KVM_SCRATCH0, offsetof(struct paca_struct,
 					   shadow_vcpu.scratch0));
 	DEFINE(PACA_KVM_SCRATCH1, offsetof(struct paca_struct,
@@ -438,6 +436,7 @@ int main(void)
 	DEFINE(VCPU_TRAMPOLINE_LOWMEM, offsetof(struct kvm_vcpu, arch.trampoline_lowmem));
 	DEFINE(VCPU_TRAMPOLINE_ENTER, offsetof(struct kvm_vcpu, arch.trampoline_enter));
 	DEFINE(VCPU_HIGHMEM_HANDLER, offsetof(struct kvm_vcpu, arch.highmem_handler));
+	DEFINE(VCPU_RMCALL, offsetof(struct kvm_vcpu, arch.rmcall));
 	DEFINE(VCPU_HFLAGS, offsetof(struct kvm_vcpu, arch.hflags));
 #else
 	DEFINE(VCPU_CR, offsetof(struct kvm_vcpu, arch.cr));
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index 3e06eae3f2c8..13173922b678 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -919,6 +919,7 @@ struct kvm_vcpu *kvmppc_core_vcpu_create(struct kvm *kvm, unsigned int id)
 	vcpu->arch.trampoline_lowmem = kvmppc_trampoline_lowmem;
 	vcpu->arch.trampoline_enter = kvmppc_trampoline_enter;
 	vcpu->arch.highmem_handler = (ulong)kvmppc_handler_highmem;
+	vcpu->arch.rmcall = *(ulong*)kvmppc_rmcall;
 
 	vcpu->arch.shadow_msr = MSR_USER64;
 
diff --git a/arch/powerpc/kvm/book3s_64_exports.c b/arch/powerpc/kvm/book3s_64_exports.c
index 5b2db38ed86c..99b07125c529 100644
--- a/arch/powerpc/kvm/book3s_64_exports.c
+++ b/arch/powerpc/kvm/book3s_64_exports.c
@@ -22,3 +22,4 @@
 
 EXPORT_SYMBOL_GPL(kvmppc_trampoline_enter);
 EXPORT_SYMBOL_GPL(kvmppc_trampoline_lowmem);
+EXPORT_SYMBOL_GPL(kvmppc_rmcall);
diff --git a/arch/powerpc/kvm/book3s_64_interrupts.S b/arch/powerpc/kvm/book3s_64_interrupts.S
index 3c0ba5513077..33aef5345f6b 100644
--- a/arch/powerpc/kvm/book3s_64_interrupts.S
+++ b/arch/powerpc/kvm/book3s_64_interrupts.S
@@ -95,17 +95,14 @@ kvm_start_entry:
 	ld	r3, VCPU_HIGHMEM_HANDLER(r4)
 	std	r3, PACA_KVM_VMHANDLER(r13)
 
-	ld	r3, VCPU_TRAMPOLINE_ENTER(r4)
-	std	r3, PACA_KVM_RMHANDLER(r13)
-
 kvm_start_lightweight:
 
 	ld	r9, VCPU_PC(r4)			/* r9 = vcpu->arch.pc */
 	ld	r10, VCPU_SHADOW_MSR(r4)	/* r10 = vcpu->arch.shadow_msr */
 
 	/* Load some guest state in the respective registers */
-	ld	r3, VCPU_CTR(r4)	/* r3 = vcpu->arch.ctr */
-	mtctr	r3			/* CTR = r3 */
+	ld	r5, VCPU_CTR(r4)	/* r5 = vcpu->arch.ctr */
+					/* will be swapped in by rmcall */
 
 	ld	r3, VCPU_LR(r4)		/* r3 = vcpu->arch.lr */
 	mtlr	r3			/* LR = r3 */
@@ -131,22 +128,14 @@ kvm_start_lightweight:
 
 no_dcbz32_on:
 
-	/* This sets the Magic value for the trampoline */
-
-	/* XXX this needs to move into a safe function, so we can
-	   be sure we don't get any interrupts */
-
-	li	r11, 1
-	stb	r11, PACA_KVM_IN_GUEST(r13)
-
-	ld	r3, PACA_KVM_RMHANDLER(r13)
-	mtsrr0	r3
+	ld	r6, VCPU_RMCALL(r4)
+	mtctr	r6
 
-	LOAD_REG_IMMEDIATE(r3, MSR_KERNEL & ~(MSR_IR | MSR_DR))
-	mtsrr1	r3
+	ld	r3, VCPU_TRAMPOLINE_ENTER(r4)
+	LOAD_REG_IMMEDIATE(r4, MSR_KERNEL & ~(MSR_IR | MSR_DR))
 
 	/* Jump to SLB patching handlder and into our guest */
-	RFI
+	bctr
 
 /*
  * This is the handler in module memory. It gets jumped at from the
diff --git a/arch/powerpc/kvm/book3s_64_rmhandlers.S b/arch/powerpc/kvm/book3s_64_rmhandlers.S
index 9ad1c2645d6f..e7091c9459a8 100644
--- a/arch/powerpc/kvm/book3s_64_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_64_rmhandlers.S
@@ -140,6 +140,24 @@ kvmppc_handler_lowmem_trampoline:
 	blr
 kvmppc_handler_lowmem_trampoline_end:
 
+/*
+ * Call a function in real mode
+ *
+ * Input Registers:
+ *
+ * R3 = function
+ * R4 = MSR
+ * R5 = CTR
+ *
+ */
+_GLOBAL(kvmppc_rmcall)
+	mtmsr	r4		/* Disable relocation, so mtsrr
+				   doesn't get interrupted */
+	mtctr	r5
+	mtsrr0	r3
+	mtsrr1	r4
+	RFI
+
 .global kvmppc_trampoline_lowmem
 kvmppc_trampoline_lowmem:
 	.long kvmppc_handler_lowmem_trampoline - _stext
diff --git a/arch/powerpc/kvm/book3s_64_slb.S b/arch/powerpc/kvm/book3s_64_slb.S
index d07b88617b2c..35b762722187 100644
--- a/arch/powerpc/kvm/book3s_64_slb.S
+++ b/arch/powerpc/kvm/book3s_64_slb.S
@@ -63,6 +63,10 @@ kvmppc_handler_trampoline_enter:
 	mtsrr0	r9
 	mtsrr1	r10
 
+	/* Activate guest mode, so faults get handled by KVM */
+	li	r11, KVM_GUEST_MODE_GUEST
+	stb	r11, PACA_KVM_IN_GUEST(r13)
+
 	/* Remove LPAR shadow entries */
 
 #if SLB_NUM_BOLTED == 3