x86/boot: Make the GDT 8-byte aligned

The segment descriptors are loaded with an implicitly LOCK-ed instruction,
which could trigger the split lock #AC exception if the variable is not
properly aligned and crosses a cache line.

Align the GDT properly so the descriptors are all 8 byte aligned.

Signed-off-by: Xiaoyao Li <xiaoyao.li@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Link: https://lkml.kernel.org/r/20190627045525.105266-1-xiaoyao.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index fafb75c..6233ae3 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -659,6 +659,7 @@ no_longmode:
 gdt64:
        .word   gdt_end - gdt
        .quad   0
+       .balign 8
 gdt:
        .word   gdt_end - gdt
        .long   gdt