[Xen-changelog] [xen stable-4.9] x86/vmx: Don't clobber %dr6 while debugging state is lazy

[patchbot@xxxxxxx]

commit c6055c559c64d41467c1e0d28af30ff18e9f260b
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jul 30 11:55:08 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jul 30 11:55:08 2018 +0200

    x86/vmx: Don't clobber %dr6 while debugging state is lazy
    
    c/s 4f36452b63 introduced a write to %dr6 in the #DB intercept case, but the
    guests debug registers may be lazy at this point, at which point the guests
    later attempt to read %dr6 will discard this value and use the older stale
    value.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    master commit: 3cdac2805692c7accde2f405d81cc0be799aee48
    master date: 2018-07-19 14:06:48 +0100
---
 xen/arch/x86/hvm/vmx/vmx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 13a31660cd..bbe2e52e21 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -3750,6 +3750,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
              */
             __vmread(EXIT_QUALIFICATION, &exit_qualification);
             HVMTRACE_1D(TRAP_DEBUG, exit_qualification);
+            __restore_debug_registers(v);
             write_debugreg(6, exit_qualification | DR_STATUS_RESERVED_ONE);
             if ( !v->domain->debugger_attached )
             {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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