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Re: [Qemu-devel] ppc64 not resuming with v2.3.0-rc3


From: Stefan Berger
Subject: Re: [Qemu-devel] ppc64 not resuming with v2.3.0-rc3
Date: Thu, 16 Apr 2015 15:49:46 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 04/16/2015 03:42 PM, Mark Cave-Ayland wrote:
On 16/04/15 17:43, Stefan Berger wrote:

The culprit patch seems to be the following commit. If I remove these
changes from the tip of the tree it works again (on SLOF level):

commit 2360b6e84f78d41fa0f76555a947148b73645259
Author: Mark Cave-Ayland <address@hidden>
Date:   Mon Feb 9 22:40:48 2015 +0000

     target-ppc: force update of msr bits in cpu_post_load

     Since env->msr has already been restored by the time cpu_post_load
is called,
     make sure that ppc_store_msr() is explicitly called with all msr
bits except
     MSR_TGPR marked as invalid.

     This solves the issue where MSR flags aren't set correctly when
restoring a VM
     snapshot, in particular the internal env->excp_prefix value when
MSR_EP has
     been altered by a guest.

     Signed-off-by: Mark Cave-Ayland <address@hidden>
     Signed-off-by: Alexander Graf <address@hidden>

diff --git a/target-ppc/machine.c b/target-ppc/machine.c
index c801b82..3921012 100644
--- a/target-ppc/machine.c
+++ b/target-ppc/machine.c
@@ -159,6 +159,7 @@ static int cpu_post_load(void *opaque, int version_id)
      PowerPCCPU *cpu = opaque;
      CPUPPCState *env = &cpu->env;
      int i;
+    target_ulong msr;

      /*
       * We always ignore the source PVR. The user or management
@@ -190,7 +191,12 @@ static int cpu_post_load(void *opaque, int version_id)
          /* Restore htab_base and htab_mask variables */
          ppc_store_sdr1(env, env->spr[SPR_SDR1]);
      }
-    hreg_compute_hflags(env);
+
+    /* Mark msr bits except MSR_TGPR invalid before restoring */
+    msr = env->msr;
+    env->msr ^= ~(1ULL << MSR_TGPR);
+    ppc_store_msr(env, msr);
+
      hreg_compute_mem_idx(env);

      return 0;


    Stefan

PS: Sorry for the late notice (-rc3), but I only started doing things
with ppc64 a few days ago.
Hmmmm the fix is correct in that internal MSR variables need to be
updated post-restore (as noted in the message above it was the exception
prefix variables that weren't updated by having MSR_EP set).

Maybe on ppc64 there is another bit similar to MSR_TGPR that needs to be
excluded? Alex, any thoughts?

I want to add that I am running QEMU for ppc64 in emulation mode on a x86_64 host. The suspend/resume problem, while in SLOF, did not exist in QEMU v2.2, so I anticipate that this is a regression would also be visible on QEMU on kvm, though a simple test on such a machine may show different...

Removing the patch solves the problem while in SLOF. Once booting into Linux suspend/resume does not work - with qemu-system-ppc64 on x86_64 host. Timestamps shown by Linux actually make a jump backwards and ultimately Linux hangs.


     Stefan



ATB,

Mark.






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