x86: fix XCR0 handling

- both VMX and SVM ignored the ECX input to XSETBV
- both SVM and VMX used the full 64-bit RAX when calculating the input
  mask to XSETBV
- faults on XSETBV did not get recovered from

Also consolidate the handling for PV and HVM into a single function,
and make the per-CPU variable "xcr0" static to xstate.c.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 5c89197692..48f3487102 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1332,8 +1332,9 @@ static void __context_switch(void)
     if ( !is_idle_vcpu(n) )
     {
         memcpy(stack_regs, &n->arch.user_regs, CTXT_SWITCH_STACK_BYTES);
-        if ( xsave_enabled(n) && n->arch.xcr0 != get_xcr0() )
-            set_xcr0(n->arch.xcr0);
+        if ( xsave_enabled(n) && n->arch.xcr0 != get_xcr0() &&
+             !set_xcr0(n->arch.xcr0) )
+            BUG();
         vcpu_restore_fpu_eager(n);
         n->arch.ctxt_switch_to(n);
     }