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Re: [Xen-devel] [RFC Patch v3 18/18] x86/hvm: Always set pending event injection when loading VMC[BS] state.

On 9/5/2014 4:11 AM, Wen Congyang wrote:
In colo mode, secondary vm is running, so VM_ENTRY_INTR_INFO may
valid before restoring vmcs. If there is no pending event after
restoring vm, we should clear it.

Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>

Also clear pending software exceptions.
Copy the fix to SVM as well.

Signed-off-by: Tim Deegan <tim@xxxxxxx>

vmx part:
Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

svm part:
Cc: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@xxxxxxx>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
  xen/arch/x86/hvm/svm/svm.c | 15 ++++++++-------
  xen/arch/x86/hvm/vmx/vmx.c | 25 ++++++++++++-------------
  2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index b5188e6..053e511 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -321,16 +321,17 @@ static int svm_vmcb_restore(struct vcpu *v, struct 
hvm_hw_cpu *c)
          vmcb_set_h_cr3(vmcb, pagetable_get_paddr(p2m_get_pagetable(p2m)));
- if ( c->pending_valid )
+    if ( c->pending_valid &&
+         hvm_event_needs_reinjection(c->pending_type, c->pending_vector) )
          gdprintk(XENLOG_INFO, "Re-injecting %#"PRIx32", %#"PRIx32"\n",
                   c->pending_event, c->error_code);
-        if ( hvm_event_needs_reinjection(c->pending_type, c->pending_vector) )
-        {
-            vmcb->eventinj.bytes = c->pending_event;
-            vmcb->eventinj.fields.errorcode = c->error_code;
-        }
+        vmcb->eventinj.bytes = c->pending_event;
+        vmcb->eventinj.fields.errorcode = c->error_code;
+    }
+    else
+    {
+        vmcb->eventinj.bytes = 0;
vmcb->cleanbits.bytes = 0;

You mention that this 'fix' is just copied for svm. But you have not seen the problem of "VM_ENTRY_INTR_INFO may be valid" (whose svm equivalent is "vmcb->eventinj.bytes is valid"). My concern is that we should test colo mode for svm first, since, if the problem is never really seen on svm, then fix may not be _necessary_

At this point, my problems are with test setups. I can help testing scenarios, but as Wen had mentioned, 'colo testing' might be the way to test. So, if I can get some pointers to how I can reproduce the issue at hand, then it would be very helpful.

(Tim had mentioned we could try to simulate it by running a guest that takes lot of faults and save-restore another guest over it. However, I am not having much luck following this route. I got a hvm guest to continuously take SW exceptions on all vcpus and tried to save-restore.
I can't see vmcb->eventinj.bytes containing any valid info.)


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