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Commit 565977a3 authored by Toshi Kani's avatar Toshi Kani Committed by Thomas Gleixner
Browse files

x86/mm: Remove pointless checks in vmalloc_fault 



vmalloc_fault() sets user's pgd or p4d from the kernel page table.  Once
it's set, all tables underneath are identical. There is no point of
following the same page table with two separate pointers and make sure they
see the same with BUG().

Remove the pointless checks in vmalloc_fault(). Also rename the kernel
pgd/p4d pointers to pgd_k/p4d_k so that their names are consistent in the
file.

Suggested-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarToshi Kani <toshi.kani@hpe.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Gratian Crisan <gratian.crisan@ni.com>
Link: https://lkml.kernel.org/r/20180314205932.7193-1-toshi.kani@hpe.com
parent 745dd37f

arch/x86/mm/fault.c

+17 −39
Original line number Diff line number Diff line
@@ -417,11 +417,11 @@ void vmalloc_sync_all(void) 
 */

static noinline int vmalloc_fault(unsigned long address)

{

	pgd_t *pgd, *pgd_ref;

	p4d_t *p4d, *p4d_ref;

	pud_t *pud, *pud_ref;

	pmd_t *pmd, *pmd_ref;

	pte_t *pte, *pte_ref;

	pgd_t *pgd, *pgd_k;

	p4d_t *p4d, *p4d_k;

	pud_t *pud;

	pmd_t *pmd;

	pte_t *pte;



	/* Make sure we are in vmalloc area: */

	if (!(address >= VMALLOC_START && address < VMALLOC_END))
@@ -435,73 +435,51 @@ static noinline int vmalloc_fault(unsigned long address) 
	 * case just flush:

	 */

	pgd = (pgd_t *)__va(read_cr3_pa()) + pgd_index(address);

	pgd_ref = pgd_offset_k(address);

	if (pgd_none(*pgd_ref))

	pgd_k = pgd_offset_k(address);

	if (pgd_none(*pgd_k))

		return -1;



	if (pgtable_l5_enabled) {

		if (pgd_none(*pgd)) {

			set_pgd(pgd, *pgd_ref);

			set_pgd(pgd, *pgd_k);

			arch_flush_lazy_mmu_mode();

		} else {

			BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));

			BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_k));

		}

	}



	/* With 4-level paging, copying happens on the p4d level. */

	p4d = p4d_offset(pgd, address);

	p4d_ref = p4d_offset(pgd_ref, address);

	if (p4d_none(*p4d_ref))

	p4d_k = p4d_offset(pgd_k, address);

	if (p4d_none(*p4d_k))

		return -1;



	if (p4d_none(*p4d) && !pgtable_l5_enabled) {

		set_p4d(p4d, *p4d_ref);

		set_p4d(p4d, *p4d_k);

		arch_flush_lazy_mmu_mode();

	} else {

		BUG_ON(p4d_pfn(*p4d) != p4d_pfn(*p4d_ref));

		BUG_ON(p4d_pfn(*p4d) != p4d_pfn(*p4d_k));

	}



	/*

	 * Below here mismatches are bugs because these lower tables

	 * are shared:

	 */

	BUILD_BUG_ON(CONFIG_PGTABLE_LEVELS < 4);



	pud = pud_offset(p4d, address);

	pud_ref = pud_offset(p4d_ref, address);

	if (pud_none(*pud_ref))

	if (pud_none(*pud))

		return -1;



	if (pud_none(*pud) || pud_pfn(*pud) != pud_pfn(*pud_ref))

		BUG();



	if (pud_large(*pud))

		return 0;



	pmd = pmd_offset(pud, address);

	pmd_ref = pmd_offset(pud_ref, address);

	if (pmd_none(*pmd_ref))

	if (pmd_none(*pmd))

		return -1;



	if (pmd_none(*pmd) || pmd_pfn(*pmd) != pmd_pfn(*pmd_ref))

		BUG();



	if (pmd_large(*pmd))

		return 0;



	pte_ref = pte_offset_kernel(pmd_ref, address);

	if (!pte_present(*pte_ref))

		return -1;



	pte = pte_offset_kernel(pmd, address);



	/*

	 * Don't use pte_page here, because the mappings can point

	 * outside mem_map, and the NUMA hash lookup cannot handle

	 * that:

	 */

	if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))

		BUG();

	if (!pte_present(*pte))

		return -1;



	return 0;

}