[Xen-devel] [PATCH v2] xstate: make use_xsave non-init

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

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.
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>
---
 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 3293ef834f..1dddda2818 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -577,7 +577,11 @@ 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 use_xsave = true;
     boolean_param("xsave", use_xsave);
 
     bool bsp = c == &boot_cpu_data;
-- 
2.22.0


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