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Date:   Fri, 24 Nov 2017 10:14:09 +0100
From:   Ingo Molnar <>
Cc:     Dave Hansen <>,
        Andy Lutomirski <>,
        Thomas Gleixner <>,
        "H . Peter Anvin" <>,
        Peter Zijlstra <>,
        Borislav Petkov <>,
        Linus Torvalds <>
Subject: [PATCH 04/43] x86/gdt: Put per-cpu GDT remaps in ascending order

From: Andy Lutomirski <>

We currently have CPU 0's GDT at the top of the GDT range and
higher-numbered CPUs at lower addresses.  This happens because the
fixmap is upside down (index 0 is the top of the fixmap).

Flip it so that GDTs are in ascending order by virtual address.
This will simplify a future patch that will generalize the GDT
remap to contain multiple pages.

Signed-off-by: Andy Lutomirski <>
Reviewed-by: Borislav Petkov <>
Reviewed-by: Thomas Gleixner <>
Cc: Borislav Petkov <>
Cc: Borislav Petkov <>
Cc: Brian Gerst <>
Cc: Dave Hansen <>
Cc: Denys Vlasenko <>
Cc: H. Peter Anvin <>
Cc: Josh Poimboeuf <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Signed-off-by: Ingo Molnar <>
 arch/x86/include/asm/desc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 4011cb03ef08..95cd95eb7285 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -63,7 +63,7 @@ static inline struct desc_struct *get_current_gdt_rw(void)
 /* Get the fixmap index for a specific processor */
 static inline unsigned int get_cpu_gdt_ro_index(int cpu)
-	return FIX_GDT_REMAP_BEGIN + cpu;
+	return FIX_GDT_REMAP_END - cpu;
 /* Provide the fixmap address of the remapped GDT */

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