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authorDaniel Vetter <daniel.vetter@ffwll.ch>2021-03-16 16:33:03 +0100
committerDaniel Vetter <daniel.vetter@ffwll.ch>2021-04-08 16:54:38 +0200
commitac8b8400620a4b0d9ca903ee9ad440bec736f5fa (patch)
tree9496daecd86a4acd64fa9a1f1a6c01357627124c
parent3f7448dde3364e30c6aa169930e88f0f2f0f00ac (diff)
mm: unexport follow_pfntopic/iomem-mmap-vs-gup-2021-05-03
Both kvm (in bd2fae8da794 ("KVM: do not assume PTE is writable after follow_pfn")) and vfio (in 07956b6269d3 ("vfio/type1: Use follow_pte()")) have lost their callsites of follow_pfn(). All the other ones have been switched over to unsafe_follow_pfn because they cannot be fixed without breaking userspace api. Argueably the vfio and kvm code is still racy, but that's kinda a bigger picture. But since it does leak the pte beyond where it drops the pt lock, without anything else like an mmu notifier guaranteeing coherence, the problem is at least clearly visible in the vfio code. So good enough with me. I've decided to keep the explanation that after dropping the pt lock you must have an mmu notifier if you keep using the pte somehow by adjusting it and moving it into the kerneldoc for the new follow_pte() function. Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: 3pvd@google.com Cc: Jann Horn <jannh@google.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Cornelia Huck <cohuck@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: linux-mm@kvack.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-samsung-soc@vger.kernel.org Cc: linux-media@vger.kernel.org Cc: kvm@vger.kernel.org Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20210316153303.3216674-4-daniel.vetter@ffwll.ch
-rw-r--r--include/linux/mm.h2
-rw-r--r--mm/memory.c26
-rw-r--r--mm/nommu.c13
3 files changed, 6 insertions, 35 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index caec8b25d66f..304588e2f829 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1693,8 +1693,6 @@ int follow_invalidate_pte(struct mm_struct *mm, unsigned long address,
pmd_t **pmdpp, spinlock_t **ptlp);
int follow_pte(struct mm_struct *mm, unsigned long address,
pte_t **ptepp, spinlock_t **ptlp);
-int follow_pfn(struct vm_area_struct *vma, unsigned long address,
- unsigned long *pfn);
int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address,
unsigned long *pfn);
int follow_phys(struct vm_area_struct *vma, unsigned long address,
diff --git a/mm/memory.c b/mm/memory.c
index e8a145505b69..317e653c8aeb 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4724,7 +4724,10 @@ out:
* should be taken for read.
*
* KVM uses this function. While it is arguably less bad than ``follow_pfn``,
- * it is not a good general-purpose API.
+ * it is not a good general-purpose API: If callers use the pte after they've
+ * unlocked @ptlp they must ensure coherency with pte updates by using a
+ * &mmu_notifier to follow updates. Any caller not following these requirements
+ * must use unsafe_follow_pfn() instead.
*
* Return: zero on success, -ve otherwise.
*/
@@ -4735,25 +4738,7 @@ int follow_pte(struct mm_struct *mm, unsigned long address,
}
EXPORT_SYMBOL_GPL(follow_pte);
-/**
- * follow_pfn - look up PFN at a user virtual address
- * @vma: memory mapping
- * @address: user virtual address
- * @pfn: location to store found PFN
- *
- * Only IO mappings and raw PFN mappings are allowed. Note that callers must
- * ensure coherency with pte updates by using a &mmu_notifier to follow updates.
- * If this is not feasible, or the access to the @pfn is only very short term,
- * use follow_pte_pmd() instead and hold the pagetable lock for the duration of
- * the access instead. Any caller not following these requirements must use
- * unsafe_follow_pfn() instead.
- *
- * This function does not allow the caller to read the permissions
- * of the PTE. Do not use it.
- *
- * Return: zero and the pfn at @pfn on success, -ve otherwise.
- */
-int follow_pfn(struct vm_area_struct *vma, unsigned long address,
+static int follow_pfn(struct vm_area_struct *vma, unsigned long address,
unsigned long *pfn)
{
int ret = -EINVAL;
@@ -4770,7 +4755,6 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address,
pte_unmap_unlock(ptep, ptl);
return 0;
}
-EXPORT_SYMBOL_GPL(follow_pfn);
/**
* unsafe_follow_pfn - look up PFN at a user virtual address
diff --git a/mm/nommu.c b/mm/nommu.c
index 1dc983f50e2c..cee29d0791b3 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -111,17 +111,7 @@ unsigned int kobjsize(const void *objp)
return page_size(page);
}
-/**
- * follow_pfn - look up PFN at a user virtual address
- * @vma: memory mapping
- * @address: user virtual address
- * @pfn: location to store found PFN
- *
- * Only IO mappings and raw PFN mappings are allowed.
- *
- * Returns zero and the pfn at @pfn on success, -ve otherwise.
- */
-int follow_pfn(struct vm_area_struct *vma, unsigned long address,
+static int follow_pfn(struct vm_area_struct *vma, unsigned long address,
unsigned long *pfn)
{
if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
@@ -130,7 +120,6 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address,
*pfn = address >> PAGE_SHIFT;
return 0;
}
-EXPORT_SYMBOL_GPL(follow_pfn);
/**
* unsafe_follow_pfn - look up PFN at a user virtual address