[Xen-changelog] [xen-4.0-testing] svm: Avoid VINTR injection during NMI shadow

["Xen patchbot-4.0-testing" <patchbot-4.0-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1273481754 -3600
# Node ID 0349638790b4f2821e91d5d845ffca3a2567bde2
# Parent  6b5eb168e3f963e68af126643647cb0236c5905c
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 6b5eb168e3f9 -r 0349638790b4 xen/arch/x86/hvm/svm/intr.c
--- a/xen/arch/x86/hvm/svm/intr.c       Mon May 10 09:55:28 2010 +0100
+++ b/xen/arch/x86/hvm/svm/intr.c       Mon May 10 09:55:54 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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