From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58775) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1CkR-0007wM-UR for qemu-devel@nongnu.org; Mon, 22 Jul 2013 05:49:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V1CkQ-0006in-LA for qemu-devel@nongnu.org; Mon, 22 Jul 2013 05:49:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38982) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1CkQ-0006iH-EL for qemu-devel@nongnu.org; Mon, 22 Jul 2013 05:49:42 -0400 Message-ID: <51ED0025.7090805@redhat.com> Date: Mon, 22 Jul 2013 11:49:25 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1374475799-18523-1-git-send-email-owasserm@redhat.com> In-Reply-To: <1374475799-18523-1-git-send-email-owasserm@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/2] Fix real mode guest migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Orit Wasserman Cc: aliguori@us.ibm.com, ehabkost@redhat.com, gleb@redhat.com, mtosatti@redhat.com, qemu-devel@nongnu.org, afaerber@suse.de Il 22/07/2013 08:49, Orit Wasserman ha scritto: > 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 > --- > 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). > + */ Coding standard asks for *s on every line. As discussed offlist, I would prefer to have this in the kernel since that's where the bug is. Gleb disagrees. We need to find a third person who mediates... Anthony, Eduardo, what do you think? Paolo > + 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; >