mm: remove follow_pte()

JIRA: https://issues.redhat.com/browse/RHEL-73613

commit b0a1c0d
Author: Peter Xu <peterx@redhat.com>
Date:   Mon Aug 26 16:43:50 2024 -0400

    mm: remove follow_pte()

    follow_pte() users have been converted to follow_pfnmap*().  Remove the
    API.

    Link: https://lkml.kernel.org/r/20240826204353.2228736-17-peterx@redhat.com
    Signed-off-by: Peter 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: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Donald Dutile <ddutile@redhat.com>

Author: ddutile

include/linux/mm.h

@@ -2369,8 +2369,6 @@ void free_pgd_range(struct mmu_gather *tlb, unsigned long addr,
 		unsigned long end, unsigned long floor, unsigned long ceiling);
 int
 copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma);
-int follow_pte(struct vm_area_struct *vma, unsigned long address,
-	       pte_t **ptepp, spinlock_t **ptlp);
 int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
 			void *buf, int len, int write);
 

mm/memory.c

@@ -5606,79 +5606,6 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 }
 #endif /* __PAGETABLE_PMD_FOLDED */
 
-/**
- * follow_pte - look up PTE at a user virtual address
- * @vma: the memory mapping
- * @address: user virtual address
- * @ptepp: location to store found PTE
- * @ptlp: location to store the lock for the PTE
- *
- * On a successful return, the pointer to the PTE is stored in @ptepp;
- * the corresponding lock is taken and its location is stored in @ptlp.
- *
- * The contents of the PTE are only stable until @ptlp is released using
- * pte_unmap_unlock(). This function will fail if the PTE is non-present.
- * Present PTEs may include PTEs that map refcounted pages, such as
- * anonymous folios in COW mappings.
- *
- * Callers must be careful when relying on PTE content after
- * pte_unmap_unlock(). Especially if the PTE maps a refcounted page,
- * callers must protect against invalidation with MMU notifiers; otherwise
- * access to the PFN at a later point in time can trigger use-after-free.
- *
- * Only IO mappings and raw PFN mappings are allowed.  The mmap semaphore
- * should be taken for read.
- *
- * This function must not be used to modify PTE content.
- *
- * Return: zero on success, -ve otherwise.
- */
-int follow_pte(struct vm_area_struct *vma, unsigned long address,
-	       pte_t **ptepp, spinlock_t **ptlp)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	pgd_t *pgd;
-	p4d_t *p4d;
-	pud_t *pud;
-	pmd_t *pmd;
-	pte_t *ptep;
-
-	mmap_assert_locked(mm);
-	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
-		goto out;
-
-	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
-		goto out;
-
-	pgd = pgd_offset(mm, address);
-	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
-		goto out;
-
-	p4d = p4d_offset(pgd, address);
-	if (p4d_none(*p4d) || unlikely(p4d_bad(*p4d)))
-		goto out;
-
-	pud = pud_offset(p4d, address);
-	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
-		goto out;
-
-	pmd = pmd_offset(pud, address);
-	VM_BUG_ON(pmd_trans_huge(*pmd));
-
-	ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
-	if (!ptep)
-		goto out;
-	if (!pte_present(ptep_get(ptep)))
-		goto unlock;
-	*ptepp = ptep;
-	return 0;
-unlock:
-	pte_unmap_unlock(ptep, *ptlp);
-out:
-	return -EINVAL;
-}
-EXPORT_SYMBOL_GPL(follow_pte);
-
 static inline void pfnmap_args_setup(struct follow_pfnmap_args *args,
 				     spinlock_t *lock, pte_t *ptep,
 				     pgprot_t pgprot, unsigned long pfn_base,