Commit bc02afbd authored by Peter Xu's avatar Peter Xu Committed by Andrew Morton
Browse files

mm/fork: accept huge pfnmap entries 

Teach the fork code to properly copy pfnmaps for pmd/pud levels.  Pud is
much easier, the write bit needs to be persisted though for writable and
shared pud mappings like PFNMAP ones, otherwise a follow up write in
either parent or child process will trigger a write fault.

Do the same for pmd level.

Link: https://lkml.kernel.org/r/20240826204353.2228736-8-peterx@redhat.com


Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 10d83d77

mm/huge_memory.c

+26 −3
Original line number Diff line number Diff line
@@ -1583,6 +1583,24 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
	pgtable_t pgtable = NULL;

	int ret = -ENOMEM;



	pmd = pmdp_get_lockless(src_pmd);

	if (unlikely(pmd_special(pmd))) {

		dst_ptl = pmd_lock(dst_mm, dst_pmd);

		src_ptl = pmd_lockptr(src_mm, src_pmd);

		spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);

		/*

		 * No need to recheck the pmd, it can't change with write

		 * mmap lock held here.

		 *

		 * Meanwhile, making sure it's not a CoW VMA with writable

		 * mapping, otherwise it means either the anon page wrongly

		 * applied special bit, or we made the PRIVATE mapping be

		 * able to wrongly write to the backend MMIO.

		 */

		VM_WARN_ON_ONCE(is_cow_mapping(src_vma->vm_flags) && pmd_write(pmd));

		goto set_pmd;

	}



	/* Skip if can be re-fill on fault */

	if (!vma_is_anonymous(dst_vma))

		return 0;
@@ -1664,7 +1682,9 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
	pmdp_set_wrprotect(src_mm, addr, src_pmd);

	if (!userfaultfd_wp(dst_vma))

		pmd = pmd_clear_uffd_wp(pmd);

	pmd = pmd_mkold(pmd_wrprotect(pmd));

	pmd = pmd_wrprotect(pmd);

set_pmd:

	pmd = pmd_mkold(pmd);

	set_pmd_at(dst_mm, addr, dst_pmd, pmd);



	ret = 0;
@@ -1710,8 +1730,11 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
	 * TODO: once we support anonymous pages, use

	 * folio_try_dup_anon_rmap_*() and split if duplicating fails.

	 */

	if (is_cow_mapping(vma->vm_flags) && pud_write(pud)) {

		pudp_set_wrprotect(src_mm, addr, src_pud);

	pud = pud_mkold(pud_wrprotect(pud));

		pud = pud_wrprotect(pud);

	}

	pud = pud_mkold(pud);

	set_pud_at(dst_mm, addr, dst_pud, pud);



	ret = 0;