diff mbox series

[09/13] gup: Don't allow FOLL_LONGTERM pinning of FS DAX pages

Message ID 74a9fc9e018e54d7afbeae166479e2358e0a1225.1719386613.git-series.apopple@nvidia.com
State Not Applicable
Headers show
Series fs/dax: Fix FS DAX page reference counts | expand

Commit Message

Alistair Popple June 27, 2024, 12:54 a.m. UTC 
Longterm pinning of FS DAX pages should already be disallowed by
various pXX_devmap checks. However a future change will cause these
checks to be invalid for FS DAX pages so make
folio_is_longterm_pinnable() return false for FS DAX pages.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 include/linux/memremap.h | 11 +++++++++++
 include/linux/mm.h       |  4 ++++
 2 files changed, 15 insertions(+)

Comments

David Hildenbrand July 1, 2024, 8:59 a.m. UTC | #1 
On 27.06.24 02:54, Alistair Popple wrote:
> Longterm pinning of FS DAX pages should already be disallowed by
> various pXX_devmap checks. However a future change will cause these
> checks to be invalid for FS DAX pages so make
> folio_is_longterm_pinnable() return false for FS DAX pages.
> 
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ---
>   include/linux/memremap.h | 11 +++++++++++
>   include/linux/mm.h       |  4 ++++
>   2 files changed, 15 insertions(+)
> 
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 6505713..19a448e 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -193,6 +193,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
>   	return is_device_coherent_page(&folio->page);
>   }
>   
> +static inline bool is_device_dax_page(const struct page *page)
> +{
> +	return is_zone_device_page(page) &&
> +		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
> +}
> +
> +static inline bool folio_is_device_dax(const struct folio *folio)
> +{
> +	return is_device_dax_page(&folio->page);
> +}
> +
>   #ifdef CONFIG_ZONE_DEVICE
>   void zone_device_page_init(struct page *page);
>   void *memremap_pages(struct dev_pagemap *pgmap, int nid);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b84368b..4d1cdea 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2032,6 +2032,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>   	if (folio_is_device_coherent(folio))
>   		return false;
>   
> +	/* DAX must also always allow eviction. */
> +	if (folio_is_device_dax(folio))
> +		return false;
> +
>   	/* Otherwise, non-movable zone folios can be pinned. */
>   	return !folio_is_zone_movable(folio);
>   

Why is the check in check_vma_flags() insufficient? GUP-fast maybe?
Alistair Popple July 1, 2024, 11:47 p.m. UTC | #2 
David Hildenbrand <david@redhat.com> writes:

> On 27.06.24 02:54, Alistair Popple wrote:
>> Longterm pinning of FS DAX pages should already be disallowed by
>> various pXX_devmap checks. However a future change will cause these
>> checks to be invalid for FS DAX pages so make
>> folio_is_longterm_pinnable() return false for FS DAX pages.
>> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>> ---
>>   include/linux/memremap.h | 11 +++++++++++
>>   include/linux/mm.h       |  4 ++++
>>   2 files changed, 15 insertions(+)
>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>> index 6505713..19a448e 100644
>> --- a/include/linux/memremap.h
>> +++ b/include/linux/memremap.h
>> @@ -193,6 +193,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
>>   	return is_device_coherent_page(&folio->page);
>>   }
>>   +static inline bool is_device_dax_page(const struct page *page)
>> +{
>> +	return is_zone_device_page(page) &&
>> +		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
>> +}
>> +
>> +static inline bool folio_is_device_dax(const struct folio *folio)
>> +{
>> +	return is_device_dax_page(&folio->page);
>> +}
>> +
>>   #ifdef CONFIG_ZONE_DEVICE
>>   void zone_device_page_init(struct page *page);
>>   void *memremap_pages(struct dev_pagemap *pgmap, int nid);
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index b84368b..4d1cdea 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2032,6 +2032,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>>   	if (folio_is_device_coherent(folio))
>>   		return false;
>>   +	/* DAX must also always allow eviction. */
>> +	if (folio_is_device_dax(folio))
>> +		return false;
>> +
>>   	/* Otherwise, non-movable zone folios can be pinned. */
>>   	return !folio_is_zone_movable(folio);
>>   
>
> Why is the check in check_vma_flags() insufficient? GUP-fast maybe?

Right. This came up when I was changing the code for GUP-fast, but also
they shouldn't be longterm pinnable and adding the case to
folio_is_longterm_pinnable() is an excellent way of documenting that.
David Hildenbrand July 2, 2024, 10:48 a.m. UTC | #3 
On 02.07.24 01:47, Alistair Popple wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 27.06.24 02:54, Alistair Popple wrote:
>>> Longterm pinning of FS DAX pages should already be disallowed by
>>> various pXX_devmap checks. However a future change will cause these
>>> checks to be invalid for FS DAX pages so make
>>> folio_is_longterm_pinnable() return false for FS DAX pages.
>>> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>>> ---
>>>    include/linux/memremap.h | 11 +++++++++++
>>>    include/linux/mm.h       |  4 ++++
>>>    2 files changed, 15 insertions(+)
>>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>>> index 6505713..19a448e 100644
>>> --- a/include/linux/memremap.h
>>> +++ b/include/linux/memremap.h
>>> @@ -193,6 +193,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
>>>    	return is_device_coherent_page(&folio->page);
>>>    }
>>>    +static inline bool is_device_dax_page(const struct page *page)
>>> +{
>>> +	return is_zone_device_page(page) &&
>>> +		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
>>> +}
>>> +
>>> +static inline bool folio_is_device_dax(const struct folio *folio)
>>> +{
>>> +	return is_device_dax_page(&folio->page);
>>> +}
>>> +
>>>    #ifdef CONFIG_ZONE_DEVICE
>>>    void zone_device_page_init(struct page *page);
>>>    void *memremap_pages(struct dev_pagemap *pgmap, int nid);
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index b84368b..4d1cdea 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -2032,6 +2032,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>>>    	if (folio_is_device_coherent(folio))
>>>    		return false;
>>>    +	/* DAX must also always allow eviction. */
>>> +	if (folio_is_device_dax(folio))
>>> +		return false;
>>> +
>>>    	/* Otherwise, non-movable zone folios can be pinned. */
>>>    	return !folio_is_zone_movable(folio);
>>>    
>>
>> Why is the check in check_vma_flags() insufficient? GUP-fast maybe?
> 
> Right. This came up when I was changing the code for GUP-fast, but also
> they shouldn't be longterm pinnable and adding the case to
> folio_is_longterm_pinnable() is an excellent way of documenting that.

Makes sense, might be worth adding that (GUP-fast and check_vma_flags() 
covering GUP-slow) to the patch description.
diff mbox series

Patch

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 6505713..19a448e 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -193,6 +193,17 @@  static inline bool folio_is_device_coherent(const struct folio *folio)
 	return is_device_coherent_page(&folio->page);
 }
 
+static inline bool is_device_dax_page(const struct page *page)
+{
+	return is_zone_device_page(page) &&
+		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
+}
+
+static inline bool folio_is_device_dax(const struct folio *folio)
+{
+	return is_device_dax_page(&folio->page);
+}
+
 #ifdef CONFIG_ZONE_DEVICE
 void zone_device_page_init(struct page *page);
 void *memremap_pages(struct dev_pagemap *pgmap, int nid);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b84368b..4d1cdea 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2032,6 +2032,10 @@  static inline bool folio_is_longterm_pinnable(struct folio *folio)
 	if (folio_is_device_coherent(folio))
 		return false;
 
+	/* DAX must also always allow eviction. */
+	if (folio_is_device_dax(folio))
+		return false;
+
 	/* Otherwise, non-movable zone folios can be pinned. */
 	return !folio_is_zone_movable(folio);