From 6da8e9634bb7e3fdad9ae0e4db873a05036c4343 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Mon, 26 Aug 2024 16:43:43 -0400 Subject: [PATCH] mm: new follow_pfnmap API Introduce a pair of APIs to follow pfn mappings to get entry information. It's very similar to what follow_pte() does before, but different in that it recognizes huge pfn mappings. Link: https://lkml.kernel.org/r/20240826204353.2228736-10-peterx@redhat.com Signed-off-by: Peter Xu Cc: Alexander Gordeev Cc: Alex Williamson Cc: Aneesh Kumar K.V Cc: Borislav Petkov Cc: Catalin Marinas Cc: Christian Borntraeger Cc: Dave Hansen Cc: David Hildenbrand Cc: Gavin Shan Cc: Gerald Schaefer Cc: Heiko Carstens Cc: Ingo Molnar Cc: Jason Gunthorpe Cc: Matthew Wilcox Cc: Niklas Schnelle Cc: Paolo Bonzini Cc: Ryan Roberts Cc: Sean Christopherson Cc: Sven Schnelle Cc: Thomas Gleixner Cc: Vasily Gorbik Cc: Will Deacon Cc: Zi Yan Signed-off-by: Andrew Morton --- include/linux/mm.h | 31 ++++++++++ mm/memory.c | 150 +++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 181 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index c2307a2d275d..62bd89414897 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2373,6 +2373,37 @@ int follow_pte(struct vm_area_struct *vma, unsigned long address, int generic_access_phys(struct vm_area_struct *vma, unsigned long addr, void *buf, int len, int write); +struct follow_pfnmap_args { + /** + * Inputs: + * @vma: Pointer to @vm_area_struct struct + * @address: the virtual address to walk + */ + struct vm_area_struct *vma; + unsigned long address; + /** + * Internals: + * + * The caller shouldn't touch any of these. + */ + spinlock_t *lock; + pte_t *ptep; + /** + * Outputs: + * + * @pfn: the PFN of the address + * @pgprot: the pgprot_t of the mapping + * @writable: whether the mapping is writable + * @special: whether the mapping is a special mapping (real PFN maps) + */ + unsigned long pfn; + pgprot_t pgprot; + bool writable; + bool special; +}; +int follow_pfnmap_start(struct follow_pfnmap_args *args); +void follow_pfnmap_end(struct follow_pfnmap_args *args); + extern void truncate_pagecache(struct inode *inode, loff_t new); extern void truncate_setsize(struct inode *inode, loff_t newsize); void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to); diff --git a/mm/memory.c b/mm/memory.c index 9a540e231625..3878bf69bc14 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -6172,6 +6172,156 @@ out: } 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, + unsigned long addr_mask, bool writable, + bool special) +{ + args->lock = lock; + args->ptep = ptep; + args->pfn = pfn_base + ((args->address & ~addr_mask) >> PAGE_SHIFT); + args->pgprot = pgprot; + args->writable = writable; + args->special = special; +} + +static inline void pfnmap_lockdep_assert(struct vm_area_struct *vma) +{ +#ifdef CONFIG_LOCKDEP + struct address_space *mapping = vma->vm_file->f_mapping; + + if (mapping) + lockdep_assert(lockdep_is_held(&vma->vm_file->f_mapping->i_mmap_rwsem) || + lockdep_is_held(&vma->vm_mm->mmap_lock)); + else + lockdep_assert(lockdep_is_held(&vma->vm_mm->mmap_lock)); +#endif +} + +/** + * follow_pfnmap_start() - Look up a pfn mapping at a user virtual address + * @args: Pointer to struct @follow_pfnmap_args + * + * The caller needs to setup args->vma and args->address to point to the + * virtual address as the target of such lookup. On a successful return, + * the results will be put into other output fields. + * + * After the caller finished using the fields, the caller must invoke + * another follow_pfnmap_end() to proper releases the locks and resources + * of such look up request. + * + * During the start() and end() calls, the results in @args will be valid + * as proper locks will be held. After the end() is called, all the fields + * in @follow_pfnmap_args will be invalid to be further accessed. Further + * use of such information after end() may require proper synchronizations + * by the caller with page table updates, otherwise it can create a + * security bug. + * + * If the PTE maps a refcounted page, callers are responsible to 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, and the mmap semaphore cannot be released + * before the end() is invoked. + * + * This function must not be used to modify PTE content. + * + * Return: zero on success, negative otherwise. + */ +int follow_pfnmap_start(struct follow_pfnmap_args *args) +{ + struct vm_area_struct *vma = args->vma; + unsigned long address = args->address; + struct mm_struct *mm = vma->vm_mm; + spinlock_t *lock; + pgd_t *pgdp; + p4d_t *p4dp, p4d; + pud_t *pudp, pud; + pmd_t *pmdp, pmd; + pte_t *ptep, pte; + + pfnmap_lockdep_assert(vma); + + if (unlikely(address < vma->vm_start || address >= vma->vm_end)) + goto out; + + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) + goto out; +retry: + pgdp = pgd_offset(mm, address); + if (pgd_none(*pgdp) || unlikely(pgd_bad(*pgdp))) + goto out; + + p4dp = p4d_offset(pgdp, address); + p4d = READ_ONCE(*p4dp); + if (p4d_none(p4d) || unlikely(p4d_bad(p4d))) + goto out; + + pudp = pud_offset(p4dp, address); + pud = READ_ONCE(*pudp); + if (pud_none(pud)) + goto out; + if (pud_leaf(pud)) { + lock = pud_lock(mm, pudp); + if (!unlikely(pud_leaf(pud))) { + spin_unlock(lock); + goto retry; + } + pfnmap_args_setup(args, lock, NULL, pud_pgprot(pud), + pud_pfn(pud), PUD_MASK, pud_write(pud), + pud_special(pud)); + return 0; + } + + pmdp = pmd_offset(pudp, address); + pmd = pmdp_get_lockless(pmdp); + if (pmd_leaf(pmd)) { + lock = pmd_lock(mm, pmdp); + if (!unlikely(pmd_leaf(pmd))) { + spin_unlock(lock); + goto retry; + } + pfnmap_args_setup(args, lock, NULL, pmd_pgprot(pmd), + pmd_pfn(pmd), PMD_MASK, pmd_write(pmd), + pmd_special(pmd)); + return 0; + } + + ptep = pte_offset_map_lock(mm, pmdp, address, &lock); + if (!ptep) + goto out; + pte = ptep_get(ptep); + if (!pte_present(pte)) + goto unlock; + pfnmap_args_setup(args, lock, ptep, pte_pgprot(pte), + pte_pfn(pte), PAGE_MASK, pte_write(pte), + pte_special(pte)); + return 0; +unlock: + pte_unmap_unlock(ptep, lock); +out: + return -EINVAL; +} +EXPORT_SYMBOL_GPL(follow_pfnmap_start); + +/** + * follow_pfnmap_end(): End a follow_pfnmap_start() process + * @args: Pointer to struct @follow_pfnmap_args + * + * Must be used in pair of follow_pfnmap_start(). See the start() function + * above for more information. + */ +void follow_pfnmap_end(struct follow_pfnmap_args *args) +{ + if (args->lock) + spin_unlock(args->lock); + if (args->ptep) + pte_unmap(args->ptep); +} +EXPORT_SYMBOL_GPL(follow_pfnmap_end); + #ifdef CONFIG_HAVE_IOREMAP_PROT /** * generic_access_phys - generic implementation for iomem mmap access