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Date: Fri, 20 Sep 2019 10:21:32 +0800
From: Jia He <justin.he@....com>
To: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>,
James Morse <james.morse@....com>,
Marc Zyngier <maz@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Suzuki Poulose <Suzuki.Poulose@....com>
Cc: Punit Agrawal <punitagrawal@...il.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Jun Yao <yaojun8558363@...il.com>,
Alex Van Brunt <avanbrunt@...dia.com>,
Robin Murphy <robin.murphy@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Jérôme Glisse <jglisse@...hat.com>,
Ralph Campbell <rcampbell@...dia.com>, hejianet@...il.com,
Kaly Xin <Kaly.Xin@....com>, Jia He <justin.he@....com>
Subject: [PATCH v6 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
When we tested pmdk unit test [1] vmmalloc_fork TEST1 in arm64 guest, there
will be a double page fault in __copy_from_user_inatomic of cow_user_page.
Below call trace is from arm64 do_page_fault for debugging purpose
[ 110.016195] Call trace:
[ 110.016826] do_page_fault+0x5a4/0x690
[ 110.017812] do_mem_abort+0x50/0xb0
[ 110.018726] el1_da+0x20/0xc4
[ 110.019492] __arch_copy_from_user+0x180/0x280
[ 110.020646] do_wp_page+0xb0/0x860
[ 110.021517] __handle_mm_fault+0x994/0x1338
[ 110.022606] handle_mm_fault+0xe8/0x180
[ 110.023584] do_page_fault+0x240/0x690
[ 110.024535] do_mem_abort+0x50/0xb0
[ 110.025423] el0_da+0x20/0x24
The pte info before __copy_from_user_inatomic is (PTE_AF is cleared):
[ffff9b007000] pgd=000000023d4f8003, pud=000000023da9b003, pmd=000000023d4b3003, pte=360000298607bd3
As told by Catalin: "On arm64 without hardware Access Flag, copying from
user will fail because the pte is old and cannot be marked young. So we
always end up with zeroed page after fork() + CoW for pfn mappings. we
don't always have a hardware-managed access flag on arm64."
This patch fix it by calling pte_mkyoung. Also, the parameter is
changed because vmf should be passed to cow_user_page()
Add a WARN_ON_ONCE when __copy_from_user_inatomic() returns error
in case there can be some obscure use-case.(by Kirill)
[1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork
Reported-by: Yibo Cai <Yibo.Cai@....com>
Signed-off-by: Jia He <justin.he@....com>
---
mm/memory.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 59 insertions(+), 6 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index e2bb51b6242e..7c38c1ce5440 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -118,6 +118,13 @@ int randomize_va_space __read_mostly =
2;
#endif
+#ifndef arch_faults_on_old_pte
+static inline bool arch_faults_on_old_pte(void)
+{
+ return false;
+}
+#endif
+
static int __init disable_randmaps(char *s)
{
randomize_va_space = 0;
@@ -2140,8 +2147,12 @@ static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
return same;
}
-static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
+static inline int cow_user_page(struct page *dst, struct page *src,
+ struct vm_fault *vmf)
{
+ struct vm_area_struct *vma = vmf->vma;
+ unsigned long addr = vmf->address;
+
debug_dma_assert_idle(src);
/*
@@ -2151,21 +2162,52 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
* fails, we just zero-fill it. Live with it.
*/
if (unlikely(!src)) {
- void *kaddr = kmap_atomic(dst);
- void __user *uaddr = (void __user *)(va & PAGE_MASK);
+ void *kaddr;
+ void __user *uaddr = (void __user *)(addr & PAGE_MASK);
+ pte_t entry;
+
+ /* On architectures with software "accessed" bits, we would
+ * take a double page fault, so mark it accessed here.
+ */
+ if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
+ spin_lock(vmf->ptl);
+ if (likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+ entry = pte_mkyoung(vmf->orig_pte);
+ if (ptep_set_access_flags(vma, addr,
+ vmf->pte, entry, 0))
+ update_mmu_cache(vma, addr, vmf->pte);
+ } else {
+ /* Other thread has already handled the fault
+ * and we don't need to do anything. If it's
+ * not the case, the fault will be triggered
+ * again on the same address.
+ */
+ spin_unlock(vmf->ptl);
+ return -1;
+ }
+ spin_unlock(vmf->ptl);
+ }
+ kaddr = kmap_atomic(dst);
/*
* This really shouldn't fail, because the page is there
* in the page tables. But it might just be unreadable,
* in which case we just give up and fill the result with
* zeroes.
*/
- if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
+ if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+ /* Give a warn in case there can be some obscure
+ * use-case
+ */
+ WARN_ON_ONCE(1);
clear_page(kaddr);
+ }
kunmap_atomic(kaddr);
flush_dcache_page(dst);
} else
- copy_user_highpage(dst, src, va, vma);
+ copy_user_highpage(dst, src, addr, vma);
+
+ return 0;
}
static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
@@ -2318,7 +2360,16 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
vmf->address);
if (!new_page)
goto oom;
- cow_user_page(new_page, old_page, vmf->address, vma);
+
+ if (cow_user_page(new_page, old_page, vmf)) {
+ /* COW failed, if the fault was solved by other,
+ * it's fine. If not, userspace would re-fault on
+ * the same address and we will handle the fault
+ * from the second attempt.
+ */
+ put_page(new_page);
+ goto normal;
+ }
}
if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false))
@@ -2420,6 +2471,8 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
}
put_page(old_page);
}
+
+normal:
return page_copied ? VM_FAULT_WRITE : 0;
oom_free_new:
put_page(new_page);
--
2.17.1
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