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From: Orit Wasserman <owasserm@redhat.com>
To: qemu-devel@nongnu.org
Cc: aliguori@us.ibm.com, ehabkost@redhat.com, gleb@redhat.com,
	mtosatti@redhat.com, Orit Wasserman <owasserm@redhat.com>,
	pbonzini@redhat.com, afaerber@suse.de
Subject: [Qemu-devel] [PATCH 1/2] Fix real mode guest migration
Date: Mon, 22 Jul 2013 09:49:58 +0300	[thread overview]
Message-ID: <1374475799-18523-1-git-send-email-owasserm@redhat.com> (raw)

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.

Signed-off-by: Orit Wasserman <owasserm@redhat.com>
---
 target-i386/machine.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/target-i386/machine.c b/target-i386/machine.c
index 3659db9..7e95829 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 worngly.
+      Fixing it will allow live migration from such host that don't have
+      restricted guest support to an 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;
-- 
1.8.1.4

             reply	other threads:[~2013-07-22  6:49 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-22  6:49 Orit Wasserman [this message]
2013-07-22  6:49 ` [Qemu-devel] [PATCH 2/2] Fix real mode guest segments dpl value in savevm Orit Wasserman
2013-07-22  9:49 ` [Qemu-devel] [PATCH 1/2] Fix real mode guest migration Paolo Bonzini
2013-07-22  9:58   ` Gleb Natapov
2013-07-22 10:10   ` Orit Wasserman
2013-07-22 10:14     ` Paolo Bonzini
2013-07-22 13:20       ` Eduardo Habkost
2013-07-22 10:33   ` Andreas Färber
2013-07-22 10:50     ` Gleb Natapov
2013-07-22 10:59     ` Orit Wasserman
2013-07-22 12:46       ` Juan Quintela
2013-07-22 17:50   ` Anthony Liguori
2013-07-22 18:50     ` Gleb Natapov
2013-07-22 10:50 ` Juan Quintela
2013-07-22 16:37 ` Eric Blake

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