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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>
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3 changed files with 18 additions and 16 deletions
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@ -39,7 +39,6 @@ extern struct desc_ptr idt_descr;
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extern gate_desc idt_table[];
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extern const struct desc_ptr debug_idt_descr;
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extern gate_desc debug_idt_table[];
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extern pgprot_t pg_fixmap_gdt_flags;
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struct gdt_page {
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struct desc_struct gdt[GDT_ENTRIES];
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@ -448,21 +448,27 @@ void load_percpu_segment(int cpu)
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load_stack_canary_segment();
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}
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/*
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* On 64-bit the GDT remapping is read-only.
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* A global is used for Xen to change the default when required.
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*/
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#ifdef CONFIG_X86_64
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pgprot_t pg_fixmap_gdt_flags = PAGE_KERNEL_RO;
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#else
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pgprot_t pg_fixmap_gdt_flags = PAGE_KERNEL;
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#endif
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/* Setup the fixmap mapping only once per-processor */
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static inline void setup_fixmap_gdt(int cpu)
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{
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__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu),
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pg_fixmap_gdt_flags);
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#ifdef CONFIG_X86_64
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/* On 64-bit systems, we use a read-only fixmap GDT. */
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pgprot_t prot = PAGE_KERNEL_RO;
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#else
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/*
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* On native 32-bit systems, the GDT cannot be read-only because
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* our double fault handler uses a task gate, and entering through
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* a task gate needs to change an available TSS to busy. If the GDT
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* is read-only, that will triple fault.
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*
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* On Xen PV, the GDT must be read-only because the hypervisor requires
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* it.
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*/
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pgprot_t prot = boot_cpu_has(X86_FEATURE_XENPV) ?
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PAGE_KERNEL_RO : PAGE_KERNEL;
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#endif
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__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
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}
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/* Load the original GDT from the per-cpu structure */
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@ -1545,9 +1545,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
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*/
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xen_initial_gdt = &per_cpu(gdt_page, 0);
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/* GDT can only be remapped RO */
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pg_fixmap_gdt_flags = PAGE_KERNEL_RO;
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xen_smp_init();
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#ifdef CONFIG_ACPI_NUMA
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