[Xen-devel] [PATCHv2] x86: map portion of kexec crash area that is within the direct map area

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: David Vrabel <david.vrabel@xxxxxxxxxx>

Commit 7113a45451a9f656deeff070e47672043ed83664 (kexec/x86: do not map
crash kernel area) causes fatal page faults when loading a crash
image.  The attempt to zero the first control page allocated from the
crash region will fault as the VA return by map_domain_page() has no
mapping.

The fault will occur on non-debug builds of Xen when the crash area is
below 5 TiB (which will be most systems).

The assumption that the crash area mapping was not used is incorrect.
map_domain_page() is used when loading an image and building the
image's page tables to temporarily map the crash area, thus the
mapping is required if the crash area is in the direct map area.

Reintroduce the mapping, but only the portions of the crash area that
are within the direct map area.

Reported-by: Don Slutz <dslutz@xxxxxxxxxxx>
Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
---
This fixes a Xen crash so is an important fix for the 4.4 release..

Changes in v2:
- merge patches into one
- add check for e > s before mapping
---
 xen/arch/x86/setup.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 4833ca3..b49256d 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1098,6 +1098,17 @@ void __init __start_xen(unsigned long mbi_p)
                          PFN_UP(mod[i].mod_end), PAGE_HYPERVISOR);
     }
 
+    if ( kexec_crash_area.size )
+    {
+        unsigned long s = PFN_DOWN(kexec_crash_area.start);
+        unsigned long e = min(s + PFN_UP(kexec_crash_area.size),
+                              PFN_UP(__pa(HYPERVISOR_VIRT_END - 1)));
+
+        if ( e > s ) 
+            map_pages_to_xen((unsigned long)__va(kexec_crash_area.start),
+                             s, e - s, PAGE_HYPERVISOR);
+    }
+
     xen_virt_end = ((unsigned long)_end + (1UL << L2_PAGETABLE_SHIFT) - 1) &
                    ~((1UL << L2_PAGETABLE_SHIFT) - 1);
     destroy_xen_mappings(xen_virt_end, XEN_VIRT_START + BOOTSTRAP_MAP_BASE);
-- 
1.7.2.5


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