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 (file)
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -334,6 +334,27 @@ static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu)
        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 @@ static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu)
        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;

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 983e5ed..27db1e6 100644 (file)
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -792,7 +792,7 @@ program_interrupt:
        }
        case BOOK3S_INTERRUPT_SYSCALL:
                if (vcpu->arch.papr_enabled &&
-                   (kvmppc_get_last_inst(vcpu) == 0x44000022) &&
+                   (kvmppc_get_last_sc(vcpu) == 0x44000022) &&
                    !(vcpu->arch.shared->msr & MSR_PR)) {
                        /* SC 1 papr hypercalls */
                        ulong cmd = kvmppc_get_gpr(vcpu, 3);