[Xen-devel] [PATCH] x86/pv: Fix the handing of writes to %dr7

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/arch/x86/traps.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 37210da..4bed9de 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);
-- 
2.1.4


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