Patch "KVM: PPC: Book3S PR: Fix illegal opcode emulation" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

KVM: PPC: Book3S PR: Fix illegal opcode emulation

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-ppc-book3s-pr-fix-illegal-opcode-emulation.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Huth <[email protected]>
Date: Wed, 18 May 2016 21:01:20 +0200
Subject: KVM: PPC: Book3S PR: Fix illegal opcode emulation

From: Thomas Huth <[email protected]>

commit 708e75a3ee750dce1072134e630d66c4e6eaf63c upstream.

If kvmppc_handle_exit_pr() calls kvmppc_emulate_instruction() to emulate one instruction (in the BOOK3S_INTERRUPT_H_EMUL_ASSIST case), it calls kvmppc_core_queue_program() afterwards if kvmppc_emulate_instruction() returned EMULATE_FAIL, so the guest gets an program interrupt for the illegal opcode.
However, the kvmppc_emulate_instruction() also tried to inject a program exception for this already, so the program interrupt gets injected twice and the return address in srr0 gets destroyed. All other callers of kvmppc_emulate_instruction() are also injecting a program interrupt, and since the callers have the right knowledge about the srr1 flags that should be used, it is the function kvmppc_emulate_instruction() that should _not_ inject program interrupts, so remove the kvmppc_core_queue_program() here.

This fixes the issue discovered by Laurent Vivier with kvm-unit-tests where the logs are filled with these messages when the test tries to execute an illegal instruction:

     Couldn't emulate instruction 0x00000000 (op 0 xop 0)
     kvmppc_handle_exit_pr: emulation at 700 failed (00000000)

---
 arch/powerpc/kvm/emulate.c |    1 -
 1 file changed, 1 deletion(-)

@@ -302,7 +302,6 @@ int kvmppc_emulate_instruction(struct kv
 			advance = 0;
 			printk(KERN_ERR "Couldn't emulate instruction 0x%08x "
 			       "(op %d xop %d)\n", inst, get_op(inst), get_xop(inst));
-			kvmppc_core_queue_program(vcpu, 0);
 		}
 	}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/kvm-ppc-book3s-pr-fix-illegal-opcode-emulation.patch