From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Thu, 22 Mar 2018 17:17:20 +0000 (+0000)
Subject: x86/pv: Fix the handing of writes to %dr7
X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~275
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=adf8feba1afa040f3a84a82953e18af02060884a;p=xen.git

x86/pv: Fix the handing of writes to %dr7

c/s 65e35549 "x86/PV: support data breakpoint extension registers"
accidentally broke the handing of writes.  The call to activate_debugregs()
doesn't write %dr7 as v->arch.debugreg[7] hasn't been updated yet, and the
break skips the intended write to %dr7.

Remove the break, causing execution to hit the write_debugreg(7, value); in
context at the bottom of the hunk, which in turn causes hardware to be updated
appropriately.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 37210da8b1..4bed9de2c1 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -2074,14 +2074,11 @@ long set_debugreg(struct vcpu *v, unsigned int reg, unsigned long value)
             /*
              * If DR7 was previously clear then we need to load all other
              * debug registers at this point as they were not restored during
-             * context switch.
+             * context switch.  Updating DR7 itself happens later.
              */
             if ( (v == curr) &&
                  !(v->arch.debugreg[7] & DR7_ACTIVE_MASK) )
-            {
                 activate_debugregs(v);
-                break;
-            }
         }
         if ( v == curr )
             write_debugreg(7, value);