[Xen-changelog] [xen stable-4.6] x86/vmx: don't clobber exception_bitmap when entering/leaving emulated real mode

[patchbot@xxxxxxx]

commit 944a3c2532f48a5a3b463601fdd578fca0be5ba9
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Feb 17 16:38:23 2016 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 17 16:38:23 2016 +0100

    x86/vmx: don't clobber exception_bitmap when entering/leaving emulated real 
mode
    
    Most updates to the exception bitmaps set or clear an individual bits.
    
    However, entering or exiting emulated real mode unilaterally clobbers it,
    leaving the exit code to recalculate what it should have been.  This is 
error
    prone, and indeed currently fails to recalculate the TRAP_no_device 
intercept
    appropriately.
    
    Instead of overwriting exception_bitmap when entering emulated real mode, 
move
    the override into vmx_update_exception_bitmap() and leave exception_bitmap
    unmodified.
    
    This means that recalculation is unnecessary, and that the use of
    vmx_fpu_leave() and vmx_update_debug_state() while in emulated real mode
    doesn't result in TRAP_no_device and TRAP_int3 being un-intercepted.
    
    This is only a functional change on hardware lacking unrestricted guest
    support.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    master commit: 78c93adf0a7f6a7abe249a63e7398ca1221a6d25
    master date: 2016-02-02 14:00:52 +0100
---
 xen/arch/x86/hvm/vmx/vmx.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index b38c1ae..b3abfc2 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -383,10 +383,13 @@ void vmx_update_secondary_exec_control(struct vcpu *v)
 
 void vmx_update_exception_bitmap(struct vcpu *v)
 {
+    u32 bitmap = unlikely(v->arch.hvm_vmx.vmx_realmode)
+        ? 0xffffffffu : v->arch.hvm_vmx.exception_bitmap;
+
     if ( nestedhvm_vcpu_in_guestmode(v) )
-        nvmx_update_exception_bitmap(v, v->arch.hvm_vmx.exception_bitmap);
+        nvmx_update_exception_bitmap(v, bitmap);
     else
-        __vmwrite(EXCEPTION_BITMAP, v->arch.hvm_vmx.exception_bitmap);
+        __vmwrite(EXCEPTION_BITMAP, bitmap);
 }
 
 static int vmx_guest_x86_mode(struct vcpu *v)
@@ -1299,8 +1302,6 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned 
int cr)
             {
                 for ( s = x86_seg_cs ; s <= x86_seg_tr ; s++ )
                     vmx_set_segment_register(v, s, &reg[s]);
-                v->arch.hvm_vmx.exception_bitmap = 0xffffffff;
-                vmx_update_exception_bitmap(v);
             }
             else 
             {
@@ -1308,13 +1309,9 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned 
int cr)
                     if ( !(v->arch.hvm_vmx.vm86_segment_mask & (1<<s)) )
                         vmx_set_segment_register(
                             v, s, &v->arch.hvm_vmx.vm86_saved_seg[s]);
-                v->arch.hvm_vmx.exception_bitmap = HVM_TRAP_MASK
-                          | (paging_mode_hap(v->domain) ?
-                             0 : (1U << TRAP_page_fault))
-                          | (1U << TRAP_no_device);
-                vmx_update_exception_bitmap(v);
-                vmx_update_debug_state(v);
             }
+
+            vmx_update_exception_bitmap(v);
         }
 
         v->arch.hvm_vcpu.hw_cr[0] =
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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