[Xen-changelog] [xen stable-4.4] x86/crash: don't use set_fixmap() in the crash path

[patchbot@xxxxxxx]

commit d568854ab62c2c6c251646074c6a49a84a06f89c
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jun 18 09:34:11 2015 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jun 18 09:34:11 2015 +0200

    x86/crash: don't use set_fixmap() in the crash path
    
    Experimentally, this can result in memory allocation, and in particular a
    failed assertion that interrupts are enabled when performing a TLB flush.
    
      (XEN) Assertion 'local_irq_is_enabled()' failed at smp.c:223
      <snip>
      (XEN) [<ffff82d08018a0d3>] flush_area_mask+0x7/0x134
      (XEN) [<ffff82d08011f7c6>] alloc_domheap_pages+0xa9/0x12a
      (XEN) [<ffff82d08011f8ab>] alloc_xenheap_pages+0x64/0xdb
      (XEN) [<ffff82d080178e08>] alloc_xen_pagetable+0x1c/0xa0
      (XEN) [<ffff82d08017926b>] virt_to_xen_l1e+0x38/0x1be
      (XEN) [<ffff82d080179bff>] map_pages_to_xen+0x80e/0xfd9
      (XEN) [<ffff82d080185a23>] __set_fixmap+0x2c/0x2e
      (XEN) [<ffff82d0801a6fd4>] machine_crash_shutdown+0x186/0x2b2
      (XEN) [<ffff82d0801172bb>] kexec_crash+0x3f/0x5b
      (XEN) [<ffff82d0801479b7>] panic+0x100/0x118
      (XEN) [<ffff82d08019002b>] set_guest_machinecheck_trapbounce+0/0x6d
      (XEN) [<ffff82d080195c15>] do_page_fault+0x40b/0x541
      (XEN) [<ffff82d0802345e0>] handle_exception_saved+0x2e/0x6c
    
    Instead, use the directmap mapping which are writable and involve far less
    complexity than set_fixmap()
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 8228055568ef195df5e0c205972a4a4c278e186b
    master date: 2015-06-03 09:26:13 +0200
---
 xen/arch/x86/crash.c |    9 +++------
 1 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index 3d03bc1..c5332a5 100644
--- a/xen/arch/x86/crash.c
+++ b/xen/arch/x86/crash.c
@@ -137,13 +137,10 @@ static void nmi_shootdown_cpus(void)
      * Ideally would be:
      *   exception_table[TRAP_nmi] = &do_nmi_crash;
      *
-     * but the exception_table is read only.  Borrow an unused fixmap entry
-     * to construct a writable mapping.
+     * but the exception_table is read only.  Access it via its directmap
+     * mappings.
      */
-    set_fixmap(FIX_TBOOT_MAP_ADDRESS, __pa(&exception_table[TRAP_nmi]));
-    write_atomic((unsigned long *)
-                 (fix_to_virt(FIX_TBOOT_MAP_ADDRESS) +
-                  ((unsigned long)&exception_table[TRAP_nmi] & ~PAGE_MASK)),
+    write_atomic((unsigned long *)__va(__pa(&exception_table[TRAP_nmi])),
                  (unsigned long)&do_nmi_crash);
 
     /* Ensure the new callback function is set before sending out the NMI. */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.4

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