Commit b23adb7d authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/xen/gdt: Use X86_FEATURE_XENPV instead of globals for the GDT fixup 



Xen imposes special requirements on the GDT.  Rather than using a
global variable for the pgprot, just use an explicit special case
for Xen -- this makes it clearer what's going on.  It also debloats
64-bit kernels very slightly.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/e9ea96abbfd6a8c87753849171bb5987ecfeb523.1490218061.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 59c58ceb

arch/x86/include/asm/desc.h

+0 −1
Original line number Diff line number Diff line
@@ -39,7 +39,6 @@ extern struct desc_ptr idt_descr; 
extern gate_desc idt_table[];

extern const struct desc_ptr debug_idt_descr;

extern gate_desc debug_idt_table[];

extern pgprot_t pg_fixmap_gdt_flags;



struct gdt_page {

	struct desc_struct gdt[GDT_ENTRIES];

arch/x86/kernel/cpu/common.c

+17 −11
Original line number Diff line number Diff line
@@ -448,21 +448,27 @@ void load_percpu_segment(int cpu) 
	load_stack_canary_segment();

}



/*

 * On 64-bit the GDT remapping is read-only.

 * A global is used for Xen to change the default when required.

 */

/* Setup the fixmap mapping only once per-processor */

static inline void setup_fixmap_gdt(int cpu)

{

#ifdef CONFIG_X86_64

pgprot_t pg_fixmap_gdt_flags = PAGE_KERNEL_RO;

	/* On 64-bit systems, we use a read-only fixmap GDT. */

	pgprot_t prot = PAGE_KERNEL_RO;

#else

pgprot_t pg_fixmap_gdt_flags = PAGE_KERNEL;

	/*

	 * On native 32-bit systems, the GDT cannot be read-only because

	 * our double fault handler uses a task gate, and entering through

	 * a task gate needs to change an available TSS to busy.  If the GDT

	 * is read-only, that will triple fault.

	 *

	 * On Xen PV, the GDT must be read-only because the hypervisor requires

	 * it.

	 */

	pgprot_t prot = boot_cpu_has(X86_FEATURE_XENPV) ?

		PAGE_KERNEL_RO : PAGE_KERNEL;

#endif



/* Setup the fixmap mapping only once per-processor */

static inline void setup_fixmap_gdt(int cpu)

{

	__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu),

		     pg_fixmap_gdt_flags);

	__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);

}



/* Load the original GDT from the per-cpu structure */

arch/x86/xen/enlighten.c

+0 −3
Original line number Diff line number Diff line
@@ -1545,9 +1545,6 @@ asmlinkage __visible void __init xen_start_kernel(void) 
	 */

	xen_initial_gdt = &per_cpu(gdt_page, 0);



	/* GDT can only be remapped RO */

	pg_fixmap_gdt_flags = PAGE_KERNEL_RO;



	xen_smp_init();



#ifdef CONFIG_ACPI_NUMA

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