[Xen-changelog] [xen staging] x86/xstate: make use_xsave non-init

[patchbot@xxxxxxx]

commit 021eb25a294c388c9b0124200bf2080c1e88eb83
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Fri Sep 6 17:04:39 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Sep 6 17:04:39 2019 +0200

    x86/xstate: make use_xsave non-init
    
    LLVM code generation can attempt to load from a variable in the next
    condition of an expression under certain circumstances, thus
    attempting to load use_xsave regardless of the value of the bsp
    variable, which leads to a page fault when the init section has
    already been unmapped.
    
    Fix this by making use_xsave non-init, thus preventing the page fault;
    use __read_mostly instead. The LLVM bug with the discussion about this
    issue can be found at:
    
    https://bugs.llvm.org/show_bug.cgi?id=39707
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/xstate.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index 10016a05d0..243495ed07 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -576,7 +576,11 @@ unsigned int xstate_ctxt_size(u64 xcr0)
 /* Collect the information of processor's extended state */
 void xstate_init(struct cpuinfo_x86 *c)
 {
-    static bool __initdata use_xsave = true;
+    /*
+     * NB: use_xsave cannot live in initdata because llvm might optimize
+     * reading it, see: https://bugs.llvm.org/show_bug.cgi?id=39707
+     */
+    static bool __read_mostly use_xsave = true;
     boolean_param("xsave", use_xsave);
 
     bool bsp = c == &boot_cpu_data;
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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