KVM: PPC: Book3S PR: Make instruction fetch fallback work for system calls
It turns out that if we exit the guest due to a hcall instruction (sc 1),
and the loading of the instruction in the guest exit path fails for any
reason, the call to kvmppc_ld() in kvmppc_get_last_inst() fetches the
instruction after the hcall instruction rather than the hcall itself.
This in turn means that the instruction doesn't get recognized as an
hcall in kvmppc_handle_exit_pr() but gets passed to the guest kernel
as a sc instruction. That usually results in the guest kernel getting
a return code of 38 (ENOSYS) from an hcall, which often triggers a
BUG_ON() or other failure.
This fixes the problem by adding a new variant of kvmppc_get_last_inst()
called kvmppc_get_last_sc(), which fetches the instruction if necessary
from pc - 4 rather than pc.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index 08891d0..fa19e2f 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -334,6 +334,27 @@
return r;
}
+/*
+ * Like kvmppc_get_last_inst(), but for fetching a sc instruction.
+ * Because the sc instruction sets SRR0 to point to the following
+ * instruction, we have to fetch from pc - 4.
+ */
+static inline u32 kvmppc_get_last_sc(struct kvm_vcpu *vcpu)
+{
+ ulong pc = kvmppc_get_pc(vcpu) - 4;
+ 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);
+
+ r = svcpu->last_inst;
+ svcpu_put(svcpu);
+ return r;
+}
+
static inline ulong kvmppc_get_fault_dar(struct kvm_vcpu *vcpu)
{
struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
@@ -446,6 +467,23 @@
return vcpu->arch.last_inst;
}
+/*
+ * Like kvmppc_get_last_inst(), but for fetching a sc instruction.
+ * Because the sc instruction sets SRR0 to point to the following
+ * instruction, we have to fetch from pc - 4.
+ */
+static inline u32 kvmppc_get_last_sc(struct kvm_vcpu *vcpu)
+{
+ ulong pc = kvmppc_get_pc(vcpu) - 4;
+
+ /* Load the instruction manually if it failed to do so in the
+ * exit path */
+ if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED)
+ kvmppc_ld(vcpu, &pc, sizeof(u32), &vcpu->arch.last_inst, false);
+
+ return vcpu->arch.last_inst;
+}
+
static inline ulong kvmppc_get_fault_dar(struct kvm_vcpu *vcpu)
{
return vcpu->arch.fault_dar;