patch-0008-x86-clear-per-cpu-stub-page-information-in-cpu_smpbo.patch

From 654c767b3f8f8e27562aee8622e633a1cd4f4a1b Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Thu, 9 Jan 2020 11:07:38 +0100
Subject: [PATCH 8/9] x86: clear per cpu stub page information in
 cpu_smpboot_free()

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, irrespective of whether the CPU gets parked
or removed.

Fixes: 2e6c8f182c9c50 ("x86: distinguish CPU offlining from CPU removal")
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wl@xen.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Tao Xu <tao3.xu@intel.com>
(cherry picked from commit 774901788c5614798931a1cb2e20dd8b885f97ab)
---
 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 afac724d1d33..83b3bf70b706 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -946,6 +946,8 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove)
         unmap_domain_page(stub_page);
         destroy_xen_mappings(per_cpu(stubs.addr, cpu) & PAGE_MASK,
                              (per_cpu(stubs.addr, cpu) | ~PAGE_MASK) + 1);
+        per_cpu(stubs.addr, cpu) = 0;
+        per_cpu(stubs.mfn, cpu) = 0;
         if ( i == STUBS_PER_PAGE )
             free_domheap_page(mfn_to_page(mfn));
     }
-- 
2.26.2