KVM: PPC: Use get/set for to_svcpu to help preemption

When running the 64-bit Book3s PR code without CONFIG_PREEMPT_NONE, we were
doing a few things wrong, most notably access to PACA fields without making
sure that the pointers stay stable accross the access (preempt_disable()).

This patch moves to_svcpu towards a get/put model which allows us to disable
preemption while accessing the shadow vcpu fields in the PACA. That way we
can run preemptible and everyone's happy!

Reported-by: Jörg Sommer <joerg@alea.gnuu.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

3 files changed, 71 insertions, 19 deletions

diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index 69c7377d2071..c941c21a1893 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -183,7 +183,9 @@ static inline void kvmppc_update_int_pending(struct kvm_vcpu *vcpu,
 static inline void kvmppc_set_gpr(struct kvm_vcpu *vcpu, int num, ulong val)
 {
         if ( num < 14 ) {
-                to_svcpu(vcpu)->gpr[num] = val;
+                struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+                svcpu->gpr[num] = val;
+                svcpu_put(svcpu);
                 to_book3s(vcpu)->shadow_vcpu->gpr[num] = val;
         } else
                 vcpu->arch.gpr[num] = val;
@@ -191,80 +193,120 @@ static inline void kvmppc_set_gpr(struct kvm_vcpu *vcpu, int num, ulong val)
 
 static inline ulong kvmppc_get_gpr(struct kvm_vcpu *vcpu, int num)
 {
-        if ( num < 14 )
-                return to_svcpu(vcpu)->gpr[num];
-        else
+        if ( num < 14 ) {
+                struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+                ulong r = svcpu->gpr[num];
+                svcpu_put(svcpu);
+                return r;
+        } else
                 return vcpu->arch.gpr[num];
 }
 
 static inline void kvmppc_set_cr(struct kvm_vcpu *vcpu, u32 val)
 {
-        to_svcpu(vcpu)->cr = val;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        svcpu->cr = val;
+        svcpu_put(svcpu);
         to_book3s(vcpu)->shadow_vcpu->cr = val;
 }
 
 static inline u32 kvmppc_get_cr(struct kvm_vcpu *vcpu)
 {
-        return to_svcpu(vcpu)->cr;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        u32 r;
+        r = svcpu->cr;
+        svcpu_put(svcpu);
+        return r;
 }
 
 static inline void kvmppc_set_xer(struct kvm_vcpu *vcpu, u32 val)
 {
-        to_svcpu(vcpu)->xer = val;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        svcpu->xer = val;
         to_book3s(vcpu)->shadow_vcpu->xer = val;
+        svcpu_put(svcpu);
 }
 
 static inline u32 kvmppc_get_xer(struct kvm_vcpu *vcpu)
 {
-        return to_svcpu(vcpu)->xer;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        u32 r;
+        r = svcpu->xer;
+        svcpu_put(svcpu);
+        return r;
 }
 
 static inline void kvmppc_set_ctr(struct kvm_vcpu *vcpu, ulong val)
 {
-        to_svcpu(vcpu)->ctr = val;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        svcpu->ctr = val;
+        svcpu_put(svcpu);
 }
 
 static inline ulong kvmppc_get_ctr(struct kvm_vcpu *vcpu)
 {
-        return to_svcpu(vcpu)->ctr;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        ulong r;
+        r = svcpu->ctr;
+        svcpu_put(svcpu);
+        return r;
 }
 
 static inline void kvmppc_set_lr(struct kvm_vcpu *vcpu, ulong val)
 {
-        to_svcpu(vcpu)->lr = val;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        svcpu->lr = val;
+        svcpu_put(svcpu);
 }
 
 static inline ulong kvmppc_get_lr(struct kvm_vcpu *vcpu)
 {
-        return to_svcpu(vcpu)->lr;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        ulong r;
+        r = svcpu->lr;
+        svcpu_put(svcpu);
+        return r;
 }
 
 static inline void kvmppc_set_pc(struct kvm_vcpu *vcpu, ulong val)
 {
-        to_svcpu(vcpu)->pc = val;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        svcpu->pc = val;
+        svcpu_put(svcpu);
 }
 
 static inline ulong kvmppc_get_pc(struct kvm_vcpu *vcpu)
 {
-        return to_svcpu(vcpu)->pc;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        ulong r;
+        r = svcpu->pc;
+        svcpu_put(svcpu);
+        return r;
 }
 
 static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu)
 {
         ulong pc = kvmppc_get_pc(vcpu);
-        struct kvmppc_book3s_shadow_vcpu *svcpu = to_svcpu(vcpu);
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        u32 r;
 
         /* Load the instruction manually if it failed to do so in the
          * exit path */
         if (svcpu->last_inst == KVM_INST_FETCH_FAILED)
                 kvmppc_ld(vcpu, &pc, sizeof(u32), &svcpu->last_inst, false);
 
-        return svcpu->last_inst;
+        r = svcpu->last_inst;
+        svcpu_put(svcpu);
+        return r;
 }
 
 static inline ulong kvmppc_get_fault_dar(struct kvm_vcpu *vcpu)
 {
-        return to_svcpu(vcpu)->fault_dar;
+        struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
+        ulong r;
+        r = svcpu->fault_dar;
+        svcpu_put(svcpu);
+        return r;
 }
 
 static inline bool kvmppc_critical_section(struct kvm_vcpu *vcpu)
diff --git a/arch/powerpc/include/asm/kvm_book3s_32.h b/arch/powerpc/include/asm/kvm_book3s_32.h
index de604db135f5..38040ff82063 100644
--- a/arch/powerpc/include/asm/kvm_book3s_32.h
+++ b/arch/powerpc/include/asm/kvm_book3s_32.h
@@ -20,11 +20,15 @@
 #ifndef __ASM_KVM_BOOK3S_32_H__
 #define __ASM_KVM_BOOK3S_32_H__
 
-static inline struct kvmppc_book3s_shadow_vcpu *to_svcpu(struct kvm_vcpu *vcpu)
+static inline struct kvmppc_book3s_shadow_vcpu *svcpu_get(struct kvm_vcpu *vcpu)
 {
         return to_book3s(vcpu)->shadow_vcpu;
 }
 
+static inline void svcpu_put(struct kvmppc_book3s_shadow_vcpu *svcpu)
+{
+}
+
 #define PTE_SIZE        12
 #define VSID_ALL        0
 #define SR_INVALID      0x00000001      /* VSID 1 should always be unused */
diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index d0ac94f98f9e..2054e4726ba2 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -21,10 +21,16 @@
 #define __ASM_KVM_BOOK3S_64_H__
 
 #ifdef CONFIG_KVM_BOOK3S_PR
-static inline struct kvmppc_book3s_shadow_vcpu *to_svcpu(struct kvm_vcpu *vcpu)
+static inline struct kvmppc_book3s_shadow_vcpu *svcpu_get(struct kvm_vcpu *vcpu)
 {
+        preempt_disable();
         return &get_paca()->shadow_vcpu;
 }
+
+static inline void svcpu_put(struct kvmppc_book3s_shadow_vcpu *svcpu)
+{
+        preempt_enable();
+}
 #endif
 
 #define SPAPR_TCE_SHIFT         12