[Xen-changelog] [xen stable-4.7] x86/hvm: Clobber %cs.L when LME becomes set

[patchbot@xxxxxxx]

commit a91344a3142fea5e826ac8b3ef0b623699bf5f71
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Oct 25 17:11:08 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 25 17:11:08 2016 +0200

    x86/hvm: Clobber %cs.L when LME becomes set
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: ed00f1761689ac7b9c074e9084c81e47c25d460c
    master date: 2016-10-14 12:44:29 +0100
---
 xen/arch/x86/hvm/hvm.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 80bfabf..69580cc 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2012,6 +2012,30 @@ int hvm_set_efer(uint64_t value)
         return X86EMUL_EXCEPTION;
     }
 
+    if ( (value & EFER_LME) && !(v->arch.hvm_vcpu.guest_efer & EFER_LME) )
+    {
+        struct segment_register cs;
+
+        hvm_get_segment_register(v, x86_seg_cs, &cs);
+
+        /*
+         * %cs may be loaded with both .D and .L set in legacy mode, and both
+         * are captured in the VMCS/VMCB.
+         *
+         * If a guest does this and then tries to transition into long mode,
+         * the vmentry from setting LME fails due to invalid guest state,
+         * because %cr0.PG is still clear.
+         *
+         * When LME becomes set, clobber %cs.L to keep the guest firmly in
+         * compatibility mode until it reloads %cs itself.
+         */
+        if ( cs.attr.fields.l )
+        {
+            cs.attr.fields.l = 0;
+            hvm_set_segment_register(v, x86_seg_cs, &cs);
+        }
+    }
+
     if ( nestedhvm_enabled(v->domain) && cpu_has_svm &&
        ((value & EFER_SVME) == 0 ) &&
        ((value ^ v->arch.hvm_vcpu.guest_efer) & EFER_SVME) )
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.7

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