[PATCH v4 04/19] x86/cea: Export per CPU array 'cea_exception_stacks' for KVM to use

["Xin Li (Intel)" <xin@zytor.com>]

The per CPU array 'cea_exception_stacks' points to per CPU stacks
for #DB, NMI and #DF.  It is normally referenced via the #define:
__this_cpu_ist_top_va().

FRED introduced new fields in the host-state area of the VMCS for
stack levels 1->3 (HOST_IA32_FRED_RSP[123]), each respectively
corresponding to per CPU stacks for #DB, NMI and #DF.  KVM must
populate these each time a vCPU is loaded onto a CPU.

Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
---

Change in v4:
* Rewrite the change log and add comments to the export (Dave Hansen).
---
 arch/x86/mm/cpu_entry_area.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index 575f863f3c75..bc0d687de376 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -17,6 +17,13 @@ static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage)
 #ifdef CONFIG_X86_64
 static DEFINE_PER_CPU_PAGE_ALIGNED(struct exception_stacks, exception_stacks);
 DEFINE_PER_CPU(struct cea_exception_stacks*, cea_exception_stacks);
+/*
+ * FRED introduced new fields in the host-state area of the VMCS for
+ * stack levels 1->3 (HOST_IA32_FRED_RSP[123]), each respectively
+ * corresponding to per CPU stacks for #DB, NMI and #DF.  KVM must
+ * populate these each time a vCPU is loaded onto a CPU.
+ */
+EXPORT_PER_CPU_SYMBOL(cea_exception_stacks);
 
 static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, _cea_offset);
 
-- 
2.48.1