From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: Jia He <justin.he@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-mm@kvack.org
Subject: Re: bug: data corruption introduced by commit 83d116c53058 ("mm: fix double page fault on arm64 if PTE_AF is cleared")
Date: Wed, 12 Feb 2020 01:40:38 +0300 [thread overview]
Message-ID: <20200211224038.4u6au5jwki7lofpq@box> (raw)
In-Reply-To: <x49wo8tnl6v.fsf@segfault.boston.devel.redhat.com>
On Tue, Feb 11, 2020 at 11:27:36AM -0500, Jeff Moyer wrote:
> > The real solution would be to retry __copy_from_user_inatomic() under ptl
> > if the first attempt fails. I expect it to be ugly.
>
> So long as it's correct. :)
The first attempt on the real solution is below.
Yeah, this is ugly. Any suggestion on clearing up this mess is welcome.
Jeff, could you give it a try?
diff --git a/mm/memory.c b/mm/memory.c
index 0bccc622e482..e8bfdf0d9d1d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2257,7 +2257,7 @@ static inline bool cow_user_page(struct page *dst, struct page *src,
bool ret;
void *kaddr;
void __user *uaddr;
- bool force_mkyoung;
+ bool locked = false;
struct vm_area_struct *vma = vmf->vma;
struct mm_struct *mm = vma->vm_mm;
unsigned long addr = vmf->address;
@@ -2282,11 +2282,11 @@ static inline bool cow_user_page(struct page *dst, struct page *src,
* On architectures with software "accessed" bits, we would
* take a double page fault, so mark it accessed here.
*/
- force_mkyoung = arch_faults_on_old_pte() && !pte_young(vmf->orig_pte);
- if (force_mkyoung) {
+ if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
pte_t entry;
vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+ locked = true;
if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
/*
* Other thread has already handled the fault
@@ -2310,18 +2310,37 @@ static inline bool cow_user_page(struct page *dst, struct page *src,
* zeroes.
*/
if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+ if (locked)
+ goto warn;
+
+ /* Re-validate under PTL if the page is still mapped */
+ vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+ locked = true;
+ if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+ /* The PTE changed under us. Retry page fault. */
+ ret = false;
+ goto pte_unlock;
+ }
+
/*
- * Give a warn in case there can be some obscure
- * use-case
+ * The same page can be mapped back since last copy attampt.
+ * Try to copy again under PTL.
*/
- WARN_ON_ONCE(1);
- clear_page(kaddr);
+ if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+ /*
+ * Give a warn in case there can be some obscure
+ * use-case
+ */
+warn:
+ WARN_ON_ONCE(1);
+ clear_page(kaddr);
+ }
}
ret = true;
pte_unlock:
- if (force_mkyoung)
+ if (locked)
pte_unmap_unlock(vmf->pte, vmf->ptl);
kunmap_atomic(kaddr);
flush_dcache_page(dst);
--
Kirill A. Shutemov
next prev parent reply other threads:[~2020-02-11 22:40 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-10 22:51 bug: data corruption introduced by commit 83d116c53058 ("mm: fix double page fault on arm64 if PTE_AF is cleared") Jeff Moyer
2020-02-11 4:17 ` Justin He
2020-02-11 4:29 ` Justin He
2020-02-11 16:44 ` Jeff Moyer
2020-02-11 17:33 ` Kirill A. Shutemov
2020-02-11 17:55 ` Jeff Moyer
2020-02-11 21:44 ` Kirill A. Shutemov
2020-02-11 22:01 ` Jeff Moyer
2020-02-11 22:15 ` Kirill A. Shutemov
2020-02-11 14:51 ` Kirill A. Shutemov
2020-02-11 16:27 ` Jeff Moyer
2020-02-11 22:40 ` Kirill A. Shutemov [this message]
2020-02-12 14:22 ` Jeff Moyer
2020-02-13 12:14 ` Kirill A. Shutemov
2020-02-14 21:07 ` Jeff Moyer
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