[PATCH] nestedsvm: fix lazy fpu switching causing a triple fault

[PATCH] nestedsvm: fix lazy fpu switching causing a triple fault

[Christoph Egger]

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Fix FPU switching uncovered with Hyper-V:
Do FPU switching always on the n1 vmcb rather
doing it on the current active vmcb.
The FPU state between n1 and n2 vmcb is already
synced in the vmrun and vmexit emulation.

This fixes the situation where the n2 vmcb had the
#NM intercept bit set but the virtual vmcb did not.
That means it was believed the l1 guest can handle
an #NM intercept but was actually wrong.

The result were three #GP's with error code 0x11 in
the l1 guest.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>


-- 
---to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Einsteinring 24, 85689 Dornach b. Muenchen
Geschaeftsfuehrer: Alberto Bozzo, Andrew Bowd
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632

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diff -r 0d092359d86f xen/arch/x86/hvm/svm/svm.c
--- a/xen/arch/x86/hvm/svm/svm.c	Wed Oct 26 10:32:36 2011 +0200
+++ b/xen/arch/x86/hvm/svm/svm.c	Fri Oct 28 16:25:11 2011 +0200
@@ -349,16 +349,16 @@ static int svm_load_vmcb_ctxt(struct vcp
 
 static void svm_fpu_enter(struct vcpu *v)
 {
-    struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
+    struct vmcb_struct *n1vmcb = vcpu_nestedhvm(v).nv_n1vmcx;
 
     vcpu_restore_fpu_lazy(v);
-    vmcb_set_exception_intercepts(
-        vmcb, vmcb_get_exception_intercepts(vmcb) & ~(1U << TRAP_no_device));
+    vmcb_set_exception_intercepts(n1vmcb,
+        vmcb_get_exception_intercepts(n1vmcb) & ~(1U << TRAP_no_device));
 }
 
 static void svm_fpu_leave(struct vcpu *v)
 {
-    struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
+    struct vmcb_struct *n1vmcb = vcpu_nestedhvm(v).nv_n1vmcx;
 
     ASSERT(!v->fpu_dirtied);
     ASSERT(read_cr0() & X86_CR0_TS);
@@ -372,9 +372,9 @@ static void svm_fpu_leave(struct vcpu *v
     if ( !(v->arch.hvm_vcpu.guest_cr[0] & X86_CR0_TS) )
     {
         vmcb_set_exception_intercepts(
-            vmcb,
-            vmcb_get_exception_intercepts(vmcb) | (1U << TRAP_no_device));
-        vmcb_set_cr0(vmcb, vmcb_get_cr0(vmcb) | X86_CR0_TS);
+            n1vmcb,
+            vmcb_get_exception_intercepts(n1vmcb) | (1U << TRAP_no_device));
+        vmcb_set_cr0(n1vmcb, vmcb_get_cr0(n1vmcb) | X86_CR0_TS);
     }
 }
 
@@ -1191,15 +1191,17 @@ static void svm_fpu_dirty_intercept(void
 {
     struct vcpu *v = current;
     struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
+    struct vmcb_struct *n1vmcb = vcpu_nestedhvm(v).nv_n1vmcx;
 
     svm_fpu_enter(v);
 
-    if ( nestedhvm_enabled(v->domain) && nestedhvm_vcpu_in_guestmode(v) ) {
-       /* Check if guest must make FPU ready for the nested guest */
+    if ( vmcb != n1vmcb ) {
+
+       /* Check if l1 guest must make FPU ready for the l2 guest */
        if ( v->arch.hvm_vcpu.guest_cr[0] & X86_CR0_TS )
            hvm_inject_exception(TRAP_no_device, HVM_DELIVER_NO_ERROR_CODE, 0);
        else
-           vmcb_set_cr0(vmcb, vmcb_get_cr0(vmcb) & ~X86_CR0_TS);
+           vmcb_set_cr0(n1vmcb, vmcb_get_cr0(n1vmcb) & ~X86_CR0_TS);
        return;
     }
 

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