Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
[On behalf of justin...@arm.com]
Hi Matthew
On 2019/9/20 23:53, Matthew Wilcox wrote:
On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote:
-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)
{
Can we talk about the return type here?
+ } 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.
+*/
+ pte_unmap_unlock(vmf->pte, vmf->ptl);
+ return -1;
...
+ return 0;
}
So -1 for "try again" and 0 for "succeeded".
+ if (cow_user_page(new_page, old_page, vmf)) {
Then we use it like a bool. But it's kind of backwards from a bool because
false is success.
+ /* 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);
+ if (old_page)
+ put_page(old_page);
+ return 0;
And we don't use the return value; in fact we invert it.
Would this make more sense:
static inline bool cow_user_page(struct page *dst, struct page *src,
struct vm_fault *vmf)
...
pte_unmap_unlock(vmf->pte, vmf->ptl);
return false;
...
return true;
...
if (!cow_user_page(new_page, old_page, vmf)) {
That reads more sensibly for me. We could also go with returning a
vm_fault_t, but that would be more complex than needed today, I think.
Ok, will change the return type to bool as you suggested.
Thanks
---
Cheers,
Justin (Jia He)
Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
On Fri, Sep 20, 2019 at 08:53:00AM -0700, Matthew Wilcox wrote:
> On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote:
> > -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)
> > {
>
> Can we talk about the return type here?
>
> > + } 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.
> > +*/
> > + pte_unmap_unlock(vmf->pte, vmf->ptl);
> > + return -1;
> ...
> > + return 0;
> > }
>
> So -1 for "try again" and 0 for "succeeded".
>
> > + if (cow_user_page(new_page, old_page, vmf)) {
>
> Then we use it like a bool. But it's kind of backwards from a bool because
> false is success.
>
> > + /* 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);
> > + if (old_page)
> > + put_page(old_page);
> > + return 0;
>
> And we don't use the return value; in fact we invert it.
>
> Would this make more sense:
>
> static inline bool cow_user_page(struct page *dst, struct page *src,
> struct vm_fault *vmf)
> ...
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> return false;
> ...
> return true;
> ...
> if (!cow_user_page(new_page, old_page, vmf)) {
>
> That reads more sensibly for me.
I like this idea too.
--
Kirill A. Shutemov
Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote:
> -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)
> {
Can we talk about the return type here?
> + } 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.
> + */
> + pte_unmap_unlock(vmf->pte, vmf->ptl);
> + return -1;
...
> + return 0;
> }
So -1 for "try again" and 0 for "succeeded".
> + if (cow_user_page(new_page, old_page, vmf)) {
Then we use it like a bool. But it's kind of backwards from a bool because
false is success.
> + /* 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);
> + if (old_page)
> + put_page(old_page);
> + return 0;
And we don't use the return value; in fact we invert it.
Would this make more sense:
static inline bool cow_user_page(struct page *dst, struct page *src,
struct vm_fault *vmf)
...
pte_unmap_unlock(vmf->pte, vmf->ptl);
return false;
...
return true;
...
if (!cow_user_page(new_page, old_page, vmf)) {
That reads more sensibly for me. We could also go with returning a
vm_fault_t, but that would be more complex than needed today, I think.
RE: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
Thanks for your patent review -- Cheers, Justin (Jia He) > -Original Message- > From: Kirill A. Shutemov > Sent: 2019年9月20日 22:21 > To: Justin He (Arm Technology China) > Cc: Catalin Marinas ; Will Deacon > ; Mark Rutland ; James Morse > ; Marc Zyngier ; Matthew > Wilcox ; Kirill A. Shutemov > ; linux-arm-ker...@lists.infradead.org; > linux-kernel@vger.kernel.org; linux...@kvack.org; Suzuki Poulose > ; Punit Agrawal ; > Anshuman Khandual ; Alex Van Brunt > ; Robin Murphy ; > Thomas Gleixner ; Andrew Morton foundation.org>; Jérôme Glisse ; Ralph Campbell > ; hejia...@gmail.com; Kaly Xin (Arm Technology > China) ; nd > Subject: Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is > cleared > > On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote: > > 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): > > [9b007000] pgd=00023d4f8003, pud=00023da9b003, > pmd=00023d4b3003, pte=36298607bd3 > > > > 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 > > Signed-off-by: Jia He > > Acked-by: Kirill A. Shutemov > > -- > Kirill A. Shutemov
Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote: > 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): > [9b007000] pgd=00023d4f8003, pud=00023da9b003, > pmd=00023d4b3003, pte=36298607bd3 > > 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 > Signed-off-by: Jia He Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov
[PATCH v7 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):
[9b007000] pgd=00023d4f8003, pud=00023da9b003,
pmd=00023d4b3003, pte=36298607bd3
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
Signed-off-by: Jia He
---
mm/memory.c | 67 -
1 file changed, 61 insertions(+), 6 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index e2bb51b6242e..3e39e40fee87 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 +2147,13 @@ 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;
+ struct mm_struct *mm = vma->vm_mm;
+ unsigned long addr = vmf->address;
+
debug_dma_assert_idle(src);
/*
@@ -2151,21 +2163,53 @@ 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;
+ pte_t entry;
+ void __user *uaddr = (void __user *)(addr & PAGE_MASK);
+ /* 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)) {
+ vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr,
+ >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.
+*/
+ pte_unmap_unlock(vmf->pte, vmf->ptl);
+ return -1;
+ }
+ pte_unmap_unlock(vmf->pte, 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);
