File 6835a043-x86-PV-breakpoint-reporting.patch of Package xen.39655

# Commit d965e2ee07c56c341d8896852550914d87ea5374
# Date 2025-05-27 12:21:38 +0100
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/pv: Fix breakpoint reporting

x86_merge_dr6() is not a no-op when 0 is passed in; it will discard the
previously latched breakpoint bits.

The combination of do_debug()'s manual call to x86_merge_dr6() for external
debuggers, and pv_inject_DB() calling pv_inject_event(), results in two
x86_merge_dr6() calls.

Feed the same pending_dbg in the second time.  This makes pv_inject_event()'s
update of dr6 effectively a no-op, retaining the correct breakpoint bits.

Fixes: db39fa4b27ea ("x86/pv: Fix merging of new status bits into %dr6")
Reported-by: Manuel Bouyer <bouyer@antioche.eu.org>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Manuel Bouyer <bouyer@antioche.eu.org>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -2072,7 +2072,7 @@ void do_debug(struct cpu_user_regs *regs
         return;
     }
 
-    pv_inject_DB(0 /* N/A, already merged */);
+    pv_inject_DB(dr6 ^ X86_DR6_DEFAULT);
 }
 
 /* SAF-1-safe */