[Xen-changelog] [xen stable-4.2] dbg_rw_guest_mem: need to call put_gfn in error path

[patchbot@xxxxxxx]

commit ed234b1af2bc3edb05a7597b7b89c947a94f7c8b
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jan 30 09:00:09 2014 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jan 30 09:00:09 2014 +0100

    dbg_rw_guest_mem: need to call put_gfn in error path
    
    Using a 1G hvm domU (in grub) and gdbsx:
    
    (gdb) set arch i8086
    warning: A handler for the OS ABI "GNU/Linux" is not built into this 
configuration
    of GDB.  Attempting to continue with the default i8086 settings.
    
    The target architecture is assumed to be i8086
    (gdb) target remote localhost:9999
    Remote debugging using localhost:9999
    Remote debugging from host 127.0.0.1
    0x0000d475 in ?? ()
    (gdb) x/1xh 0x6ae9168b
    
    Will reproduce this bug.
    
    With a debug=y build you will get:
    
    Assertion '!preempt_count()' failed at preempt.c:37
    
    For a debug=n build you will get a dom0 VCPU hung (at some point) in:
    
             [ffff82c4c0126eec] _write_lock+0x3c/0x50
              ffff82c4c01e43a0  __get_gfn_type_access+0x150/0x230
              ffff82c4c0158885  dbg_rw_mem+0x115/0x360
              ffff82c4c0158fc8  arch_do_domctl+0x4b8/0x22f0
              ffff82c4c01709ed  get_page+0x2d/0x100
              ffff82c4c01031aa  do_domctl+0x2ba/0x11e0
              ffff82c4c0179662  do_mmuext_op+0x8d2/0x1b20
              ffff82c4c0183598  __update_vcpu_system_time+0x288/0x340
              ffff82c4c015c719  continue_nonidle_domain+0x9/0x30
              ffff82c4c012938b  add_entry+0x4b/0xb0
              ffff82c4c02223f9  syscall_enter+0xa9/0xae
    
    And gdb output:
    
    (gdb) x/1xh 0x6ae9168b
    0x6ae9168b:     0x3024
    (gdb) x/1xh 0x6ae9168b
    0x6ae9168b:     Ignoring packet error, continuing...
    Reply contains invalid hex digit 116
    
    The 1st one worked because the p2m.lock is recursive and the PCPU
    had not yet changed.
    
    crash reports (for example):
    
    crash> mm_rwlock_t 0xffff83083f913010
    struct mm_rwlock_t {
      lock = {
        raw = {
          lock = 2147483647
        },
        debug = {<No data fields>}
      },
      unlock_level = 0,
      recurse_count = 1,
      locker = 1,
      locker_function = 0xffff82c4c022c640 <__func__.13514> 
"__get_gfn_type_access"
    }
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
    Acked-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
    master commit: 3dbab7a8bf4bef1bb2967cb3a8c7ed2146482ab3
    master date: 2014-01-10 17:45:01 +0100
---
 xen/arch/x86/debug.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/debug.c b/xen/arch/x86/debug.c
index 35f8d2e..e477ccd 100644
--- a/xen/arch/x86/debug.c
+++ b/xen/arch/x86/debug.c
@@ -63,10 +63,17 @@ dbg_hvm_va2mfn(dbgva_t vaddr, struct domain *dp, int toaddr,
     if ( p2m_is_readonly(gfntype) && toaddr )
     {
         DBGP2("kdb:p2m_is_readonly: gfntype:%x\n", gfntype);
-        return INVALID_MFN;
+        mfn = INVALID_MFN;
+    }
+    else
+        DBGP2("X: vaddr:%lx domid:%d mfn:%lx\n", vaddr, dp->domain_id, mfn);
+
+    if ( mfn == INVALID_MFN )
+    {
+        put_gfn(dp, *gfn);
+        *gfn = INVALID_GFN;
     }
 
-    DBGP2("X: vaddr:%lx domid:%d mfn:%lx\n", vaddr, dp->domain_id, mfn);
     return mfn;
 }
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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