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>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 983e5eda892f..27db1e665959 100644
--- 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);