Re: [PATCH v9 05/24] mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE

[Laurent Dufour]

On 25/03/2018 23:50, David Rientjes wrote:
> On Tue, 13 Mar 2018, Laurent Dufour wrote:
> 
>> When handling page fault without holding the mmap_sem the fetch of the
>> pte lock pointer and the locking will have to be done while ensuring
>> that the VMA is not touched in our back.
>>
>> So move the fetch and locking operations in a dedicated function.
>>
>> Signed-off-by: Laurent Dufour 
>> ---
>>  mm/memory.c | 15 +++
>>  1 file changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 8ac241b9f370..21b1212a0892 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2288,6 +2288,13 @@ int apply_to_page_range(struct mm_struct *mm, 
>> unsigned long addr,
>>  }
>>  EXPORT_SYMBOL_GPL(apply_to_page_range);
>>  
>> +static bool pte_spinlock(struct vm_fault *vmf)
> 
> inline?

You're right.
Indeed this was done in the patch 18 : "mm: Provide speculative fault
infrastructure", but this has to be done there too, I'll fix that.

> 
>> +{
>> +vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
>> +spin_lock(vmf->ptl);
>> +return true;
>> +}
>> +
>>  static bool pte_map_lock(struct vm_fault *vmf)
>>  {
>>  vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
> 
> Shouldn't pte_unmap_same() take struct vm_fault * and use the new 
> pte_spinlock()?

done in the next patch, but you already acked it..

Re: [PATCH v9 05/24] mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE

[David Rientjes]

On Tue, 13 Mar 2018, Laurent Dufour wrote:

> When handling page fault without holding the mmap_sem the fetch of the
> pte lock pointer and the locking will have to be done while ensuring
> that the VMA is not touched in our back.
> 
> So move the fetch and locking operations in a dedicated function.
> 
> Signed-off-by: Laurent Dufour 
> ---
>  mm/memory.c | 15 +++
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 8ac241b9f370..21b1212a0892 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2288,6 +2288,13 @@ int apply_to_page_range(struct mm_struct *mm, unsigned 
> long addr,
>  }
>  EXPORT_SYMBOL_GPL(apply_to_page_range);
>  
> +static bool pte_spinlock(struct vm_fault *vmf)

inline?

> +{
> + vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
> + spin_lock(vmf->ptl);
> + return true;
> +}
> +
>  static bool pte_map_lock(struct vm_fault *vmf)
>  {
>   vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,

Shouldn't pte_unmap_same() take struct vm_fault * and use the new 
pte_spinlock()?

[PATCH v9 05/24] mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE

[Laurent Dufour]

When handling page fault without holding the mmap_sem the fetch of the
pte lock pointer and the locking will have to be done while ensuring
that the VMA is not touched in our back.

So move the fetch and locking operations in a dedicated function.

Signed-off-by: Laurent Dufour 
---
 mm/memory.c | 15 +++
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 8ac241b9f370..21b1212a0892 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2288,6 +2288,13 @@ int apply_to_page_range(struct mm_struct *mm, unsigned 
long addr,
 }
 EXPORT_SYMBOL_GPL(apply_to_page_range);
 
+static bool pte_spinlock(struct vm_fault *vmf)
+{
+   vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
+   spin_lock(vmf->ptl);
+   return true;
+}
+
 static bool pte_map_lock(struct vm_fault *vmf)
 {
vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
@@ -3798,8 +3805,8 @@ static int do_numa_page(struct vm_fault *vmf)
 * validation through pte_unmap_same(). It's of NUMA type but
 * the pfn may be screwed if the read is non atomic.
 */
-   vmf->ptl = pte_lockptr(vma->vm_mm, vmf->pmd);
-   spin_lock(vmf->ptl);
+   if (!pte_spinlock(vmf))
+   return VM_FAULT_RETRY;
if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {
pte_unmap_unlock(vmf->pte, vmf->ptl);
goto out;
@@ -3992,8 +3999,8 @@ static int handle_pte_fault(struct vm_fault *vmf)
if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
return do_numa_page(vmf);
 
-   vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
-   spin_lock(vmf->ptl);
+   if (!pte_spinlock(vmf))
+   return VM_FAULT_RETRY;
entry = vmf->orig_pte;
if (unlikely(!pte_same(*vmf->pte, entry)))
goto unlock;
-- 
2.7.4