[v3,2/2] mm: fix double page fault on arm64 if PTE_AF is cleared
diff mbox series

Message ID 20190913163239.125108-3-justin.he@arm.com
State New
Headers show
Series
  • fix double page fault on arm64
Related show

Commit Message

Jia He Sept. 13, 2019, 4:32 p.m. UTC
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>
---
 mm/memory.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

Comments

Kirill A. Shutemov Sept. 16, 2019, 9:16 a.m. UTC | #1
On Sat, Sep 14, 2019 at 12:32:39AM +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>
> ---
>  mm/memory.c | 30 +++++++++++++++++++++++++-----
>  1 file changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index e2bb51b6242e..a64af6495f71 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;
> @@ -2140,7 +2147,8 @@ 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 +2160,32 @@ 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 (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
> +			spin_lock(vmf->ptl);
> +			entry = pte_mkyoung(vmf->orig_pte);

Should't you re-validate that orig_pte after re-taking ptl? It can be
stale by now.

> +			if (ptep_set_access_flags(vmf->vma, vmf->address,
> +						  vmf->pte, entry, 0))
> +				update_mmu_cache(vmf->vma, vmf->address,
> +						 vmf->pte);
> +			spin_unlock(vmf->ptl);
> +		}
> +
>  		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 +2338,7 @@ 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
> 
>
Jia He Sept. 16, 2019, 9:35 a.m. UTC | #2
Hi Kirill
> -----Original Message-----
> From: Kirill A. Shutemov <kirill@shutemov.name>
> Sent: 2019年9月16日 17:16
> To: Justin He (Arm Technology China) <Justin.He@arm.com>
> Cc: Catalin Marinas <Catalin.Marinas@arm.com>; Will Deacon
> <will@kernel.org>; Mark Rutland <Mark.Rutland@arm.com>; James Morse
> <James.Morse@arm.com>; Marc Zyngier <maz@kernel.org>; Matthew
> Wilcox <willy@infradead.org>; Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com>; linux-arm-kernel@lists.infradead.org;
> linux-kernel@vger.kernel.org; linux-mm@kvack.org; Punit Agrawal
> <punitagrawal@gmail.com>; Anshuman Khandual
> <Anshuman.Khandual@arm.com>; Jun Yao <yaojun8558363@gmail.com>;
> Alex Van Brunt <avanbrunt@nvidia.com>; Robin Murphy
> <Robin.Murphy@arm.com>; Thomas Gleixner <tglx@linutronix.de>;
> Andrew Morton <akpm@linux-foundation.org>; Jérôme Glisse
> <jglisse@redhat.com>; Ralph Campbell <rcampbell@nvidia.com>;
> hejianet@gmail.com
> Subject: Re: [PATCH v3 2/2] mm: fix double page fault on arm64 if PTE_AF
> is cleared
>
> On Sat, Sep 14, 2019 at 12:32:39AM +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>
> > ---
> >  mm/memory.c | 30 +++++++++++++++++++++++++-----
> >  1 file changed, 25 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index e2bb51b6242e..a64af6495f71 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;
> > @@ -2140,7 +2147,8 @@ 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 +2160,32 @@ 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 (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte))
> {
> > +                   spin_lock(vmf->ptl);
> > +                   entry = pte_mkyoung(vmf->orig_pte);
>
> Should't you re-validate that orig_pte after re-taking ptl? It can be
> stale by now.
Thanks, do you mean flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte))
before pte_mkyoung?

--
Cheers,
Justin (Jia He)


>
> > +                   if (ptep_set_access_flags(vmf->vma, vmf->address,
> > +                                             vmf->pte, entry, 0))
> > +                           update_mmu_cache(vmf->vma, vmf-
> >address,
> > +                                            vmf->pte);
> > +                   spin_unlock(vmf->ptl);
> > +           }
> > +
> >             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 +2338,7 @@ 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
> >
> >
>
> --
>  Kirill A. Shutemov
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
Kirill A. Shutemov Sept. 16, 2019, 2:16 p.m. UTC | #3
On Mon, Sep 16, 2019 at 09:35:21AM +0000, Justin He (Arm Technology China) wrote:
> 
> Hi Kirill
> > -----Original Message-----
> > From: Kirill A. Shutemov <kirill@shutemov.name>
> > Sent: 2019年9月16日 17:16
> > To: Justin He (Arm Technology China) <Justin.He@arm.com>
> > Cc: Catalin Marinas <Catalin.Marinas@arm.com>; Will Deacon
> > <will@kernel.org>; Mark Rutland <Mark.Rutland@arm.com>; James Morse
> > <James.Morse@arm.com>; Marc Zyngier <maz@kernel.org>; Matthew
> > Wilcox <willy@infradead.org>; Kirill A. Shutemov
> > <kirill.shutemov@linux.intel.com>; linux-arm-kernel@lists.infradead.org;
> > linux-kernel@vger.kernel.org; linux-mm@kvack.org; Punit Agrawal
> > <punitagrawal@gmail.com>; Anshuman Khandual
> > <Anshuman.Khandual@arm.com>; Jun Yao <yaojun8558363@gmail.com>;
> > Alex Van Brunt <avanbrunt@nvidia.com>; Robin Murphy
> > <Robin.Murphy@arm.com>; Thomas Gleixner <tglx@linutronix.de>;
> > Andrew Morton <akpm@linux-foundation.org>; Jérôme Glisse
> > <jglisse@redhat.com>; Ralph Campbell <rcampbell@nvidia.com>;
> > hejianet@gmail.com
> > Subject: Re: [PATCH v3 2/2] mm: fix double page fault on arm64 if PTE_AF
> > is cleared
> >
> > On Sat, Sep 14, 2019 at 12:32:39AM +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>
> > > ---
> > >  mm/memory.c | 30 +++++++++++++++++++++++++-----
> > >  1 file changed, 25 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index e2bb51b6242e..a64af6495f71 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;
> > > @@ -2140,7 +2147,8 @@ 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 +2160,32 @@ 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 (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte))
> > {
> > > +                   spin_lock(vmf->ptl);
> > > +                   entry = pte_mkyoung(vmf->orig_pte);
> >
> > Should't you re-validate that orig_pte after re-taking ptl? It can be
> > stale by now.
> Thanks, do you mean flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte))
> before pte_mkyoung?

No. You need to check pte_same(*vmf->pte, vmf->orig_pte) before modifying
anything and bail out if *vmf->pte has changed under you.

Patch
diff mbox series

diff --git a/mm/memory.c b/mm/memory.c
index e2bb51b6242e..a64af6495f71 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;
@@ -2140,7 +2147,8 @@  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 +2160,32 @@  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 (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
+			spin_lock(vmf->ptl);
+			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);
+			spin_unlock(vmf->ptl);
+		}
+
 		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 +2338,7 @@  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))