* [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared
@ 2019-09-06 13:57 Jia He
2019-09-06 14:57 ` Matthew Wilcox
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Jia He @ 2019-09-06 13:57 UTC (permalink / raw)
To: Andrew Morton, Matthew Wilcox, Jérôme Glisse,
Ralph Campbell, Jason Gunthorpe, Peter Zijlstra, Dave Airlie,
Aneesh Kumar K.V, Thomas Hellstrom, Souptick Joarder, linux-mm,
linux-kernel
Cc: Catalin Marinas, Jia He
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()
[1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork
Reported-by: Yibo Cai <Yibo.Cai@arm.com>
Signed-off-by: Jia He <justin.he@arm.com>
---
Changes
v2: remove FAULT_FLAG_WRITE when setting pte access flag (by Catalin)
mm/memory.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index e2bb51b6242e..63d4fd285e8e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2140,7 +2140,8 @@ 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 void cow_user_page(struct page *dst, struct page *src,
+ struct vm_fault *vmf)
{
debug_dma_assert_idle(src);
@@ -2152,20 +2153,30 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
*/
if (unlikely(!src)) {
void *kaddr = kmap_atomic(dst);
- void __user *uaddr = (void __user *)(va & PAGE_MASK);
+ void __user *uaddr = (void __user *)(vmf->address & PAGE_MASK);
+ pte_t entry;
/*
* 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.
+ * zeroes. If PTE_AF is cleared on arm64, it might
+ * cause double page fault. So makes pte young here
*/
+ if (!pte_young(vmf->orig_pte)) {
+ entry = pte_mkyoung(vmf->orig_pte);
+ if (ptep_set_access_flags(vmf->vma, vmf->address,
+ vmf->pte, entry, 0))
+ update_mmu_cache(vmf->vma, vmf->address,
+ vmf->pte);
+ }
+
if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
clear_page(kaddr);
kunmap_atomic(kaddr);
flush_dcache_page(dst);
} else
- copy_user_highpage(dst, src, va, vma);
+ copy_user_highpage(dst, src, vmf->address, vmf->vma);
}
static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
@@ -2318,7 +2329,7 @@ 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);
+ cow_user_page(new_page, old_page, vmf);
}
if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false))
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared
2019-09-06 13:57 [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
@ 2019-09-06 14:57 ` Matthew Wilcox
2019-09-10 9:15 ` Catalin Marinas
2019-09-09 21:27 ` Matthew Wilcox
2019-09-10 9:29 ` Kirill A. Shutemov
2 siblings, 1 reply; 6+ messages in thread
From: Matthew Wilcox @ 2019-09-06 14:57 UTC (permalink / raw)
To: Jia He
Cc: Andrew Morton, Jérôme Glisse, Ralph Campbell,
Jason Gunthorpe, Peter Zijlstra, Dave Airlie, Aneesh Kumar K.V,
Thomas Hellstrom, Souptick Joarder, linux-mm, linux-kernel,
Catalin Marinas
On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote:
> * 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.
> + * zeroes. If PTE_AF is cleared on arm64, it might
> + * cause double page fault. So makes pte young here
How about:
* zeroes. On architectures with software "accessed" bits,
* we would take a double page fault here, so mark it
* accessed here.
> */
> + if (!pte_young(vmf->orig_pte)) {
Let's guard this with:
if (arch_sw_access_bit && !pte_young(vmf->orig_pte)) {
#define arch_sw_access_bit 0
by default and have arm64 override it (either to a variable or a constant
... your choice). Also, please somebody decide on a better name than
arch_sw_access_bit.
> + entry = pte_mkyoung(vmf->orig_pte);
> + if (ptep_set_access_flags(vmf->vma, vmf->address,
> + vmf->pte, entry, 0))
This indentation is wrong; it makes vmf->pte look like part of the subsequent
statement instead of part of the condition.
> + update_mmu_cache(vmf->vma, vmf->address,
> + vmf->pte);
> + }
> +
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared
2019-09-06 13:57 [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-06 14:57 ` Matthew Wilcox
@ 2019-09-09 21:27 ` Matthew Wilcox
2019-09-10 9:08 ` Catalin Marinas
2019-09-10 9:29 ` Kirill A. Shutemov
2 siblings, 1 reply; 6+ messages in thread
From: Matthew Wilcox @ 2019-09-09 21:27 UTC (permalink / raw)
To: Jia He
Cc: Andrew Morton, Jérôme Glisse, Ralph Campbell,
Jason Gunthorpe, Peter Zijlstra, Dave Airlie, Aneesh Kumar K.V,
Thomas Hellstrom, Souptick Joarder, linux-mm, linux-kernel,
Catalin Marinas
On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote:
> + if (!pte_young(vmf->orig_pte)) {
> + entry = pte_mkyoung(vmf->orig_pte);
> + if (ptep_set_access_flags(vmf->vma, vmf->address,
> + vmf->pte, entry, 0))
> + update_mmu_cache(vmf->vma, vmf->address,
> + vmf->pte);
> + }
> +
Oh, btw, why call update_mmu_cache() here? All you've done is changed
the 'accessed' bit. What is any architecture supposed to do in response
to this?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared
2019-09-09 21:27 ` Matthew Wilcox
@ 2019-09-10 9:08 ` Catalin Marinas
0 siblings, 0 replies; 6+ messages in thread
From: Catalin Marinas @ 2019-09-10 9:08 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Jia He, Andrew Morton, Jérôme Glisse, Ralph Campbell,
Jason Gunthorpe, Peter Zijlstra, Dave Airlie, Aneesh Kumar K.V,
Thomas Hellstrom, Souptick Joarder, linux-mm, linux-kernel
On Mon, Sep 09, 2019 at 02:27:12PM -0700, Matthew Wilcox wrote:
> On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote:
> > + if (!pte_young(vmf->orig_pte)) {
> > + entry = pte_mkyoung(vmf->orig_pte);
> > + if (ptep_set_access_flags(vmf->vma, vmf->address,
> > + vmf->pte, entry, 0))
> > + update_mmu_cache(vmf->vma, vmf->address,
> > + vmf->pte);
> > + }
> > +
>
> Oh, btw, why call update_mmu_cache() here? All you've done is changed
> the 'accessed' bit. What is any architecture supposed to do in response
> to this?
For arm64 and x86 that's a no-op but an architecture with software TLBs
may preload them to avoid a subsequent fault on access after the pte was
made young.
--
Catalin
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared
2019-09-06 14:57 ` Matthew Wilcox
@ 2019-09-10 9:15 ` Catalin Marinas
0 siblings, 0 replies; 6+ messages in thread
From: Catalin Marinas @ 2019-09-10 9:15 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Jia He, Andrew Morton, Jérôme Glisse, Ralph Campbell,
Jason Gunthorpe, Peter Zijlstra, Dave Airlie, Aneesh Kumar K.V,
Thomas Hellstrom, Souptick Joarder, linux-mm, linux-kernel
On Fri, Sep 06, 2019 at 07:57:42AM -0700, Matthew Wilcox wrote:
> On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote:
> > * 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.
> > + * zeroes. If PTE_AF is cleared on arm64, it might
> > + * cause double page fault. So makes pte young here
>
> How about:
> * zeroes. On architectures with software "accessed" bits,
> * we would take a double page fault here, so mark it
> * accessed here.
>
> > */
> > + if (!pte_young(vmf->orig_pte)) {
>
> Let's guard this with:
>
> if (arch_sw_access_bit && !pte_young(vmf->orig_pte)) {
>
> #define arch_sw_access_bit 0
> by default and have arm64 override it (either to a variable or a constant
> ... your choice). Also, please somebody decide on a better name than
> arch_sw_access_bit.
I'm not good at names either (is arch_faults_on_old_pte any better?) but
I'd make this a 0 args call: arch_sw_access_bit(). This way we can make
it a static inline function on arm64 with some static label check.
--
Catalin
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared
2019-09-06 13:57 [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-06 14:57 ` Matthew Wilcox
2019-09-09 21:27 ` Matthew Wilcox
@ 2019-09-10 9:29 ` Kirill A. Shutemov
2 siblings, 0 replies; 6+ messages in thread
From: Kirill A. Shutemov @ 2019-09-10 9:29 UTC (permalink / raw)
To: Jia He
Cc: Andrew Morton, Matthew Wilcox, Jérôme Glisse,
Ralph Campbell, Jason Gunthorpe, Peter Zijlstra, Dave Airlie,
Aneesh Kumar K.V, Thomas Hellstrom, Souptick Joarder, linux-mm,
linux-kernel, Catalin Marinas
On Fri, Sep 06, 2019 at 09:57:47PM +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):
> [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()
>
> [1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork
>
> Reported-by: Yibo Cai <Yibo.Cai@arm.com>
> Signed-off-by: Jia He <justin.he@arm.com>
> ---
> Changes
> v2: remove FAULT_FLAG_WRITE when setting pte access flag (by Catalin)
>
> mm/memory.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index e2bb51b6242e..63d4fd285e8e 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2140,7 +2140,8 @@ 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 void cow_user_page(struct page *dst, struct page *src,
> + struct vm_fault *vmf)
> {
> debug_dma_assert_idle(src);
>
> @@ -2152,20 +2153,30 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
> */
> if (unlikely(!src)) {
> void *kaddr = kmap_atomic(dst);
> - void __user *uaddr = (void __user *)(va & PAGE_MASK);
> + void __user *uaddr = (void __user *)(vmf->address & PAGE_MASK);
> + pte_t entry;
>
> /*
> * 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.
> + * zeroes. If PTE_AF is cleared on arm64, it might
> + * cause double page fault. So makes pte young here
> */
> + if (!pte_young(vmf->orig_pte)) {
> + entry = pte_mkyoung(vmf->orig_pte);
> + if (ptep_set_access_flags(vmf->vma, vmf->address,
> + vmf->pte, entry, 0))
> + update_mmu_cache(vmf->vma, vmf->address,
> + vmf->pte);
> + }
> +
I don't see where you take ptl.
--
Kirill A. Shutemov
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-09-10 9:29 UTC | newest]
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2019-09-06 13:57 [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-06 14:57 ` Matthew Wilcox
2019-09-10 9:15 ` Catalin Marinas
2019-09-09 21:27 ` Matthew Wilcox
2019-09-10 9:08 ` Catalin Marinas
2019-09-10 9:29 ` Kirill A. Shutemov
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