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From c576ee9550d38273808c2055803f3a254655753e Mon Sep 17 00:00:00 2001
From: Orit Wasserman <owasserm@redhat.com>
Date: Wed, 9 Oct 2013 10:09:10 +0200
Subject: [PATCH 15/25] Fix real mode guest migration

RH-Author: Orit Wasserman <owasserm@redhat.com>
Message-id: <1381313355-15641-6-git-send-email-owasserm@redhat.com>
Patchwork-id: 54801
O-Subject: [RHEL7.0 qemu-kvm v2 05/10] Fix real mode guest migration
Bugzilla: 921465
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Juan Quintela <quintela@redhat.com>

Older KVM versions save CS dpl value to an invalid value for real mode guests
(0x3). This patch detect this situation when loading CPU state and set all the
segments dpl to zero.
This will allow migration from older KVM on host without unrestricted guest
to hosts with restricted guest support.
For example migration from a Penryn host (with kernel 2.6.32) to
a Westmere host (for real mode guest) will fail with "kvm: unhandled exit 80000021".

Signed-off-by: Orit Wasserman <owasserm@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
(cherry picked from commit 444ba6797ef6ef331fe9fd34309b1ec59caaede3)
---
 target-i386/machine.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 target-i386/machine.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/target-i386/machine.c b/target-i386/machine.c
index ecf1617..079a132 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -260,6 +260,24 @@ static int cpu_post_load(void *opaque, int version_id)
     CPUX86State *env = &cpu->env;
     int i;
 
+    /*
+     * Real mode guest segments register DPL should be zero.
+     * Older KVM version were setting it wrongly.
+     * Fixing it will allow live migration from such host that don't have
+     * restricted guest support to a host with unrestricted guest support
+     * (otherwise the migration will fail with invalid guest state
+     * error).
+     */
+    if (!(env->cr[0] & CR0_PE_MASK) &&
+        (env->segs[R_CS].flags >> DESC_DPL_SHIFT & 3) != 0) {
+        env->segs[R_CS].flags &= ~(env->segs[R_CS].flags & DESC_DPL_MASK);
+        env->segs[R_DS].flags &= ~(env->segs[R_DS].flags & DESC_DPL_MASK);
+        env->segs[R_ES].flags &= ~(env->segs[R_ES].flags & DESC_DPL_MASK);
+        env->segs[R_FS].flags &= ~(env->segs[R_FS].flags & DESC_DPL_MASK);
+        env->segs[R_GS].flags &= ~(env->segs[R_GS].flags & DESC_DPL_MASK);
+        env->segs[R_SS].flags &= ~(env->segs[R_SS].flags & DESC_DPL_MASK);
+    }
+
     /* XXX: restore FPU round state */
     env->fpstt = (env->fpus_vmstate >> 11) & 7;
     env->fpus = env->fpus_vmstate & ~0x3800;
-- 
1.7.1