Commit 6dfeaff9 authored by Peter Xu's avatar Peter Xu Committed by Linus Torvalds
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hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp 

Huge pmd sharing for hugetlbfs is racy with userfaultfd-wp because
userfaultfd-wp is always based on pgtable entries, so they cannot be
shared.

Walk the hugetlb range and unshare all such mappings if there is, right
before UFFDIO_REGISTER will succeed and return to userspace.

This will pair with want_pmd_share() in hugetlb code so that huge pmd
sharing is completely disabled for userfaultfd-wp registered range.

Link: https://lkml.kernel.org/r/20210218231206.15524-1-peterx@redhat.com


Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Price <steven.price@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 537cf30b

fs/userfaultfd.c

+4 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/sched/signal.h>

#include <linux/sched/mm.h>

#include <linux/mm.h>

#include <linux/mmu_notifier.h>

#include <linux/poll.h>

#include <linux/slab.h>

#include <linux/seq_file.h>
@@ -1449,6 +1450,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, 
		vma->vm_flags = new_flags;

		vma->vm_userfaultfd_ctx.ctx = ctx;



		if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))

			hugetlb_unshare_all_pmds(vma);



	skip:

		prev = vma;

		start = vma->vm_end;

include/linux/hugetlb.h

+3 −0
Original line number Diff line number Diff line
@@ -188,6 +188,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, 
		unsigned long address, unsigned long end, pgprot_t newprot);



bool is_hugetlb_entry_migration(pte_t pte);

void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);



#else /* !CONFIG_HUGETLB_PAGE */
@@ -369,6 +370,8 @@ static inline vm_fault_t hugetlb_fault(struct mm_struct *mm, 
	return 0;

}



static inline void hugetlb_unshare_all_pmds(struct vm_area_struct *vma) { }



#endif /* !CONFIG_HUGETLB_PAGE */

/*

 * hugepages at page global directory. If arch support

mm/hugetlb.c

+51 −0
Original line number Diff line number Diff line
@@ -5691,6 +5691,57 @@ void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason) 
	}

}



/*

 * This function will unconditionally remove all the shared pmd pgtable entries

 * within the specific vma for a hugetlbfs memory range.

 */

void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)

{

	struct hstate *h = hstate_vma(vma);

	unsigned long sz = huge_page_size(h);

	struct mm_struct *mm = vma->vm_mm;

	struct mmu_notifier_range range;

	unsigned long address, start, end;

	spinlock_t *ptl;

	pte_t *ptep;



	if (!(vma->vm_flags & VM_MAYSHARE))

		return;



	start = ALIGN(vma->vm_start, PUD_SIZE);

	end = ALIGN_DOWN(vma->vm_end, PUD_SIZE);



	if (start >= end)

		return;



	/*

	 * No need to call adjust_range_if_pmd_sharing_possible(), because

	 * we have already done the PUD_SIZE alignment.

	 */

	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,

				start, end);

	mmu_notifier_invalidate_range_start(&range);

	i_mmap_lock_write(vma->vm_file->f_mapping);

	for (address = start; address < end; address += PUD_SIZE) {

		unsigned long tmp = address;



		ptep = huge_pte_offset(mm, address, sz);

		if (!ptep)

			continue;

		ptl = huge_pte_lock(h, mm, ptep);

		/* We don't want 'address' to be changed */

		huge_pmd_unshare(mm, vma, &tmp, ptep);

		spin_unlock(ptl);

	}

	flush_hugetlb_tlb_range(vma, start, end);

	i_mmap_unlock_write(vma->vm_file->f_mapping);

	/*

	 * No need to call mmu_notifier_invalidate_range(), see

	 * Documentation/vm/mmu_notifier.rst.

	 */

	mmu_notifier_invalidate_range_end(&range);

}



#ifdef CONFIG_CMA

static bool cma_reserve_called __initdata;