[Xen-devel] [PATCH v2] xen/x86: clear per cpu stub page information in cpu_smpboot_free()

[Juergen Gross <jgross@xxxxxxxx>]

cpu_smpboot_free() removes the stubs for the cpu going offline, but it
isn't clearing the related percpu variables. This will result in
crashes when a stub page is released due to all related cpus gone
offline and one of those cpus going online later.

Fix that by clearing stubs.addr and stubs.mfn in order to allocate a
new stub page when needed.

Fixes: 2e6c8f182c9c50 ("x86: distinguish CPU offlining from CPU removal")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Wei Liu <wl@xxxxxxx>
---
 xen/arch/x86/smpboot.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 7e29704080..46c0729214 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -945,6 +945,8 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove)
                              (per_cpu(stubs.addr, cpu) | ~PAGE_MASK) + 1);
         if ( i == STUBS_PER_PAGE )
             free_domheap_page(mfn_to_page(mfn));
+        per_cpu(stubs.addr, cpu) = 0;
+        per_cpu(stubs.mfn, cpu) = 0;
     }
 
     FREE_XENHEAP_PAGE(per_cpu(compat_gdt, cpu));
-- 
2.16.4


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