[Xen-changelog] [xen-3.4-testing] svm: Avoid VINTR injection during NMI shadow

["Xen patchbot-3.4-testing" <patchbot-3.4-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1273481863 -3600
# Node ID dcd1bc011bf95818c98cedd1eee9d2fadf896d9f
# Parent  0e7d86aa33754fa34e501dea6c0636258023fb34
svm: Avoid VINTR injection during NMI shadow

It is invalid because we get vmexit via IRET interception in this
case. VINTR is unaware of NMI shadows and may vmexit early, leaving us
in an endless loop of VINTR injections and interceptions.

Signed-off-by: Wei Wang <wei.wang2@xxxxxxx>
Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
xen-unstable changeset:   21331:bbf009817ffb
xen-unstable date:        Fri May 07 19:22:28 2010 +0100
---
 xen/arch/x86/hvm/svm/intr.c |   17 ++++++++++++++---
 1 files changed, 14 insertions(+), 3 deletions(-)

diff -r 0e7d86aa3375 -r dcd1bc011bf9 xen/arch/x86/hvm/svm/intr.c
--- a/xen/arch/x86/hvm/svm/intr.c       Thu May 06 12:03:22 2010 +0100
+++ b/xen/arch/x86/hvm/svm/intr.c       Mon May 10 09:57:43 2010 +0100
@@ -88,10 +88,21 @@ static void enable_intr_window(struct vc
      * guest can accept the real interrupt.
      *
      * TODO: Better NMI handling. We need a way to skip a MOV SS interrupt
-     * shadow. This is hard to do without hardware support. We should also
-     * track 'NMI blocking' from NMI injection until IRET. This can be done
-     * quite easily in software by intercepting the unblocking IRET.
+     * shadow. This is hard to do without hardware support. Also we should
+     * not be waiting for EFLAGS.IF to become 1.
      */
+
+    /*
+     * NMI-blocking window is handled by IRET interception. We should not
+     * inject a VINTR in this case as VINTR is unaware of NMI-blocking and
+     * hence we can enter an endless loop (VINTR intercept fires, yet
+     * hvm_interrupt_blocked() still indicates NMI-blocking is active, so
+     * we inject a VINTR, ...).
+     */
+    if ( (intack.source == hvm_intsrc_nmi) &&
+         (vmcb->general1_intercepts & GENERAL1_INTERCEPT_IRET) )
+        return;
+
     intr = vmcb->vintr;
     intr.fields.irq     = 1;
     intr.fields.vector  = 0;

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