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 <owass...@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).
> + */
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;
>
