On 18.05.2016 12:53, Thomas Huth wrote:

On 18.05.2016 12:18, Thomas Huth wrote:

quoted

On 17.05.2016 19:49, Laurent Vivier wrote:

quoted

On 17/05/2016 10:37, Alexander Graf wrote:

quoted

On 05/17/2016 10:35 AM, Laurent Vivier wrote:

quoted

On 12/05/2016 16:23, Laurent Vivier wrote:

quoted

On 12/05/2016 11:27, Alexander Graf wrote:

quoted

On 05/12/2016 11:10 AM, Laurent Vivier wrote:

quoted

On 11/05/2016 13:49, Alexander Graf wrote:

quoted

On 05/11/2016 01:14 PM, Laurent Vivier wrote:

quoted

On 11/05/2016 12:35, Alexander Graf wrote:

quoted

On 03/15/2016 09:18 PM, Laurent Vivier wrote:

quoted

While writing some instruction tests for kvm-unit-tests for
powerpc,
I've found that illegal instructions are not managed correctly
with
kvm-pr,
while it is fine with kvm-hv.

When an illegal instruction (like ".long 0") is processed by
kvm-pr,
the kernel logs are filled with:

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

While the exception handler receives an interrupt for each
instruction
executed after the illegal instruction.

Signed-off-by: Laurent Vivier <redacted>
---
     arch/powerpc/kvm/book3s_emulate.c | 4 +++-
     1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_emulate.c

b/arch/powerpc/kvm/book3s_emulate.c
index 2afdb9c..4ee969d 100644

--- a/arch/powerpc/kvm/book3s_emulate.c
+++ b/arch/powerpc/kvm/book3s_emulate.c

@@ -99,7 +99,6 @@ int kvmppc_core_emulate_op_pr(struct kvm_run

*run,
struct kvm_vcpu *vcpu,
           switch (get_op(inst)) {
         case 0:
-        emulated = EMULATE_FAIL;
             if ((kvmppc_get_msr(vcpu) & MSR_LE) &&
                 (inst == swab32(inst_sc))) {
                 /*

@@ -112,6 +111,9 @@ int kvmppc_core_emulate_op_pr(struct kvm_run

*run,
struct kvm_vcpu *vcpu,
                 kvmppc_set_gpr(vcpu, 3, EV_UNIMPLEMENTED);
                 kvmppc_set_pc(vcpu, kvmppc_get_pc(vcpu) + 4);
                 emulated = EMULATE_DONE;
+        } else {
+            kvmppc_core_queue_program(vcpu, SRR1_PROGILL);

But isn't that exactly what the semantic of EMULATE_FAIL is?
Fixing it
up in book3s_emulate.c is definitely the wrong spot.

So what is the problem you're trying to solve? Is the SRR0 at the
wrong
spot or are the log messages the problem?

No, the problem is the host kernel logs are filled by the message
and
the execution hangs. And the host becomes unresponsiveness, even
after
the end of the tests.

Please, try to run kvm-unit-tests (the emulator test) on a KVM-PR
host,
and check the kernel logs (dmesg), then try to ssh to the host...

Ok, so the log messages are the problem. Please fix the message
output
then - or remove it altogether. Or if you like, create a module
parameter that allows you to emit them.

I personally think the best solution would be to just convert the
message into a trace point.

While at it, please see whether the guest can trigger similar host
log
output excess in other code paths.

The problem is not really with the log messages: they are
consequence of
the bug I try to fix.

What happens is once kvm_pr decodes an invalid instruction all the
valid
following instructions trigger a Program exception to the guest
(but are
executed correctly). It has no real consequence on big machine like
POWER8, except that the guest become very slow and the log files of
the
host are filled with messages (and qemu uses 100% of the CPU). On a
smaller machine like a  PowerMac G5, the machine becomes simply
unusable.

It's probably more related to your verbosity level of kernel messages.
If you pass loglevel=0 (or quiet) to you kernel cmdline you won't get
the messages printed to serial which is what's slowing you down.

The other problem sounds pretty severe, but the only thing your patch
does any different from the current code flow would be the patch below.
Or did I miss anything?

diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
index 5cc2e7a..4672bc2 100644
--- a/arch/powerpc/kvm/emulate.c
+++ b/arch/powerpc/kvm/emulate.c

@@ -302,7 +302,11 @@ int kvmppc_emulate_instruction(struct kvm_run

*run,
struct kvm_vcpu *vcpu)
                         advance = 0;
                         printk(KERN_ERR "Couldn't emulate instruction
0x%08x "
                                "(op %d xop %d)\n", inst, get_op(inst),
get_xop(inst));
+#ifdef CONFIG_PPC_BOOK3S
+                       kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
+#else
                         kvmppc_core_queue_program(vcpu, 0);
+#endif
                 }
         }

Do you want I send an updated patch with your changes?

Well, you reported the issue and narrowed it down, so feel free to send
it under your name :). I merely simplified your patch a bit.

Well, while I was trying to update the patch, I've re-tested this... and
it fails. I don't know what I'm doing bad now or what I did bad before
but it seems it doesn't work. :(

Thomas, could try the patch from Alex?

The patch from Alex also does not work for me.

I've now had a closer look at the code, and I think the endless loop is
caused by the fact that we try to inject a program interrupt twice here.

In kvmppc_handle_exit_pr(), the code flow looks like this:

	case BOOK3S_INTERRUPT_H_EMUL_ASSIST:
	{
		...
		er = kvmppc_emulate_instruction(run, vcpu);
		switch (er) {
			...
		case EMULATE_FAIL:
			printk(KERN_CRIT "%s: emulation at %lx failed (%08x)\n",
			       __func__, kvmppc_get_pc(vcpu), last_inst);
			kvmppc_core_queue_program(vcpu, flags);
			printk(KERN_CRIT "%s: pc = %lx \n",
			       __func__, kvmppc_get_pc(vcpu));
			r = RESUME_GUEST;
			break;
		...
	}

But when you look at the end of kvmppc_emulate_instruction(), you
can see that the interrupt has also already been injected there:

	if (emulated == EMULATE_FAIL) {
		emulated = vcpu->kvm->arch.kvm_ops->emulate_op(run, vcpu, inst,
							       &advance);
		if (emulated == EMULATE_AGAIN) {
			advance = 0;
		} else if (emulated == EMULATE_FAIL) {
			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);
		}
	}

Injecting the program interrupt twice of course destroys the
return address in SRR0, causing this strange behavior.
If I comment out the kvmppc_core_queue_program() in
kvmppc_emulate_instruction(), the endless loop is gone.

I've now also checked the other callers of kvmppc_emulate_instruction(),
and all are already trying to inject an interrupt on their own, so
removing the kvmppc_core_queue_program() from
kvmppc_emulate_instruction() sounds like the right solution for me.
I'll submit a corresponding patch...

 Thomas