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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: Andy 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2017-03-22 14:32:34 -07:00 committed by Ingo Molnar
parent 59c58ceb29
commit b23adb7d3f
3 changed files with 18 additions and 16 deletions
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1
arch/x86/include/asm/desc.h
View File

@ -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];

30
arch/x86/kernel/cpu/common.c
View File

@ -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.
*/
#ifdef CONFIG_X86_64
pgprot_t pg_fixmap_gdt_flags = PAGE_KERNEL_RO;
#else
pgprot_t pg_fixmap_gdt_flags = 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);
#ifdef CONFIG_X86_64
/* On 64-bit systems, we use a read-only fixmap GDT. */
pgprot_t prot = PAGE_KERNEL_RO;
#else
/*
* 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
__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
}
/* Load the original GDT from the per-cpu structure */

3
arch/x86/xen/enlighten.c
View File

@ -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