[PATCH][SVM] Fix 32bit Windows guest VMs save/restore

[Wei Huang <wei.huang2@amd.com>]

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The attached patch fixes the save/restore issue seen with 32bit Windows
guest VMs. The root cause is that current Xen doesn't intercept
SYSENTER-related MSRs for 32bit guest VMs. As a result, the
guest_sysenter_xxx fields contain incorrect values and shouldn't be used
for save/restore. This patch checks the LMA bit of EFER register in the
save/restore code path.

Please apply it to both Xen-4.0 and Xen-unstable trees.

Reported-by: James Harper <james.harper@bendigoit.com.au>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Acked-by: Christoph Egger <christoph.egger@amd.com>



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diff -r 5ce41defa1fa xen/arch/x86/hvm/svm/svm.c
--- a/xen/arch/x86/hvm/svm/svm.c	Wed Jan 26 16:11:41 2011 +0000
+++ b/xen/arch/x86/hvm/svm/svm.c	Sun Jan 30 23:38:00 2011 -0600
@@ -157,6 +157,7 @@
 
 static int svm_vmcb_save(struct vcpu *v, struct hvm_hw_cpu *c)
 {
+    bool_t lma = !!(v->arch.hvm_vcpu.guest_efer & EFER_LMA);
     struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
 
     c->cr0 = v->arch.hvm_vcpu.guest_cr[0];
@@ -164,9 +165,20 @@
     c->cr3 = v->arch.hvm_vcpu.guest_cr[3];
     c->cr4 = v->arch.hvm_vcpu.guest_cr[4];
 
-    c->sysenter_cs = v->arch.hvm_svm.guest_sysenter_cs;
-    c->sysenter_esp = v->arch.hvm_svm.guest_sysenter_esp;
-    c->sysenter_eip = v->arch.hvm_svm.guest_sysenter_eip;
+    /* SYSENTER MSRs aren't intercepted under 32bit mode. So the data should 
+     * be copied from VMCB save area under 32bit mode. */
+    if ( lma ) 
+    {
+        c->sysenter_cs = v->arch.hvm_svm.guest_sysenter_cs;
+        c->sysenter_esp = v->arch.hvm_svm.guest_sysenter_esp;
+        c->sysenter_eip = v->arch.hvm_svm.guest_sysenter_eip;
+    } 
+    else
+    {
+        c->sysenter_cs = vmcb->sysenter_cs;
+        c->sysenter_esp = vmcb->sysenter_esp;
+        c->sysenter_eip = vmcb->sysenter_eip;
+    }
 
     c->pending_event = 0;
     c->error_code = 0;
@@ -185,8 +197,12 @@
 {
     unsigned long mfn = 0;
     p2m_type_t p2mt;
+    bool_t lma;
     struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
     struct p2m_domain *p2m = p2m_get_hostp2m(v->domain);
+    
+    /* Note: Please make sure guest_efer been restored at this point. */
+    lma = !!(v->arch.hvm_vcpu.guest_efer & EFER_LMA);
 
     if ( c->pending_valid &&
          ((c->pending_type == 1) || (c->pending_type > 6) ||
@@ -224,9 +240,19 @@
     hvm_update_guest_cr(v, 2);
     hvm_update_guest_cr(v, 4);
 
-    v->arch.hvm_svm.guest_sysenter_cs = c->sysenter_cs;
-    v->arch.hvm_svm.guest_sysenter_esp = c->sysenter_esp;
-    v->arch.hvm_svm.guest_sysenter_eip = c->sysenter_eip;
+    /* Copy data into VMCB save area under 32bit mode */
+    if ( lma )
+    {
+        v->arch.hvm_svm.guest_sysenter_cs = c->sysenter_cs;
+        v->arch.hvm_svm.guest_sysenter_esp = c->sysenter_esp;
+        v->arch.hvm_svm.guest_sysenter_eip = c->sysenter_eip;
+    }
+    else
+    {
+        vmcb->sysenter_cs = c->sysenter_cs;
+        vmcb->sysenter_esp = c->sysenter_esp;
+        vmcb->sysenter_eip = c->sysenter_eip;
+    }
 
     if ( paging_mode_hap(v->domain) )
     {

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