[Qemu-devel] [PATCH uq/master 2/2] KVM: make XSAVE support more robust

[Paolo Bonzini <pbonzini@redhat.com>]

QEMU moves state from CPUArchState to struct kvm_xsave and back when it
invokes the KVM_*_XSAVE ioctls.  Because it doesn't treat the XSAVE
region as an opaque blob, it might be impossible to set some state on
the destination if migrating to an older version.

This patch blocks migration if it finds that unsupported bits are set
in the XSTATE_BV header field.  To make this work robustly, QEMU should
only report in env->xstate_bv those fields that will actually end up
in the migration stream.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target-i386/kvm.c     | 3 ++-
 target-i386/machine.c | 4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 749aa09..df08a4b 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -1291,7 +1291,8 @@ static int kvm_get_xsave(X86CPU *cpu)
             sizeof env->fpregs);
     memcpy(env->xmm_regs, &xsave->region[XSAVE_XMM_SPACE],
             sizeof env->xmm_regs);
-    env->xstate_bv = *(uint64_t *)&xsave->region[XSAVE_XSTATE_BV];
+    env->xstate_bv = *(uint64_t *)&xsave->region[XSAVE_XSTATE_BV] &
+            XSTATE_SUPPORTED;
     memcpy(env->ymmh_regs, &xsave->region[XSAVE_YMMH_SPACE],
             sizeof env->ymmh_regs);
     return 0;
diff --git a/target-i386/machine.c b/target-i386/machine.c
index dc81cde..9e2cfcf 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -278,6 +278,10 @@ static int cpu_post_load(void *opaque, int version_id)
     CPUX86State *env = &cpu->env;
     int i;
 
+    if (env->xstate_bv & ~XSTATE_SUPPORTED) {
+        return -EINVAL;
+    }
+ 
     /*
      * Real mode guest segments register DPL should be zero.
      * Older KVM version were setting it wrongly.
-- 
1.8.3.1