pages need to be marked as dirty before unpinned it in
unlock_pages() which was oversight. This is fixed now.
Signed-off-by: Souptick Joarder <[email protected]>
Suggested-by: John Hubbard <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Paul Durrant <[email protected]>
---
drivers/xen/privcmd.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 33677ea..f6c1543 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
{
unsigned int i;
- for (i = 0; i < nr_pages; i++)
+ for (i = 0; i < nr_pages; i++) {
+ if (!PageDirty(pages[i]))
+ set_page_dirty_lock(pages[i]);
put_page(pages[i]);
+ }
}
static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
--
1.9.1
On 06.07.20 20:16, Souptick Joarder wrote:
> pages need to be marked as dirty before unpinned it in
> unlock_pages() which was oversight. This is fixed now.
>
> Signed-off-by: Souptick Joarder <[email protected]>
> Suggested-by: John Hubbard <[email protected]>
> Cc: John Hubbard <[email protected]>
> Cc: Boris Ostrovsky <[email protected]>
> Cc: Paul Durrant <[email protected]>
> ---
> drivers/xen/privcmd.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 33677ea..f6c1543 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
> {
> unsigned int i;
>
> - for (i = 0; i < nr_pages; i++)
> + for (i = 0; i < nr_pages; i++) {
> + if (!PageDirty(pages[i]))
> + set_page_dirty_lock(pages[i]);
With put_page() directly following I think you should be able to use
set_page_dirty() instead, as there is obviously a reference to the page
existing.
> put_page(pages[i]);
> + }
> }
>
> static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>
Juergen
On Tue, Jul 7, 2020 at 3:08 PM Jürgen Groß <[email protected]> wrote:
>
> On 06.07.20 20:16, Souptick Joarder wrote:
> > pages need to be marked as dirty before unpinned it in
> > unlock_pages() which was oversight. This is fixed now.
> >
> > Signed-off-by: Souptick Joarder <[email protected]>
> > Suggested-by: John Hubbard <[email protected]>
> > Cc: John Hubbard <[email protected]>
> > Cc: Boris Ostrovsky <[email protected]>
> > Cc: Paul Durrant <[email protected]>
> > ---
> > drivers/xen/privcmd.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> > index 33677ea..f6c1543 100644
> > --- a/drivers/xen/privcmd.c
> > +++ b/drivers/xen/privcmd.c
> > @@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
> > {
> > unsigned int i;
> >
> > - for (i = 0; i < nr_pages; i++)
> > + for (i = 0; i < nr_pages; i++) {
> > + if (!PageDirty(pages[i]))
> > + set_page_dirty_lock(pages[i]);
>
> With put_page() directly following I think you should be able to use
> set_page_dirty() instead, as there is obviously a reference to the page
> existing.
Patch [3/3] will convert above codes to use unpin_user_pages_dirty_lock()
which internally do the same check. So I thought to keep linux-stable and
linux-next code in sync. John had a similar concern [1] and later agreed to keep
this check.
Shall I keep this check ? No ?
[1] https://lore.kernel.org/xen-devel/[email protected]/
>
> > put_page(pages[i]);
> > + }
> > }
> >
> > static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> >
>
> Juergen
On 07.07.20 13:30, Souptick Joarder wrote:
> On Tue, Jul 7, 2020 at 3:08 PM Jürgen Groß <[email protected]> wrote:
>>
>> On 06.07.20 20:16, Souptick Joarder wrote:
>>> pages need to be marked as dirty before unpinned it in
>>> unlock_pages() which was oversight. This is fixed now.
>>>
>>> Signed-off-by: Souptick Joarder <[email protected]>
>>> Suggested-by: John Hubbard <[email protected]>
>>> Cc: John Hubbard <[email protected]>
>>> Cc: Boris Ostrovsky <[email protected]>
>>> Cc: Paul Durrant <[email protected]>
>>> ---
>>> drivers/xen/privcmd.c | 5 ++++-
>>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
>>> index 33677ea..f6c1543 100644
>>> --- a/drivers/xen/privcmd.c
>>> +++ b/drivers/xen/privcmd.c
>>> @@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
>>> {
>>> unsigned int i;
>>>
>>> - for (i = 0; i < nr_pages; i++)
>>> + for (i = 0; i < nr_pages; i++) {
>>> + if (!PageDirty(pages[i]))
>>> + set_page_dirty_lock(pages[i]);
>>
>> With put_page() directly following I think you should be able to use
>> set_page_dirty() instead, as there is obviously a reference to the page
>> existing.
>
> Patch [3/3] will convert above codes to use unpin_user_pages_dirty_lock()
> which internally do the same check. So I thought to keep linux-stable and
> linux-next code in sync. John had a similar concern [1] and later agreed to keep
> this check.
>
> Shall I keep this check ? No ?
>
> [1] https://lore.kernel.org/xen-devel/[email protected]/
I wasn't referring to checking PageDirty(), but to the use of
set_page_dirty_lock().
Looking at the comment just before the implementation of
set_page_dirty_lock() suggests that it is fine to use set_page_dirty()
instead (so not calling lock_page()).
Only the transition from get_user_pages_fast() to pin_user_pages_fast()
requires to use the locked version IMO.
Juergen
On 2020-07-07 04:43, Jürgen Groß wrote:
> On 07.07.20 13:30, Souptick Joarder wrote:
>> On Tue, Jul 7, 2020 at 3:08 PM Jürgen Groß <[email protected]> wrote:
...
>>>> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
>>>> index 33677ea..f6c1543 100644
>>>> --- a/drivers/xen/privcmd.c
>>>> +++ b/drivers/xen/privcmd.c
>>>> @@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
>>>> {
>>>> unsigned int i;
>>>>
>>>> - for (i = 0; i < nr_pages; i++)
>>>> + for (i = 0; i < nr_pages; i++) {
>>>> + if (!PageDirty(pages[i]))
>>>> + set_page_dirty_lock(pages[i]);
>>>
>>> With put_page() directly following I think you should be able to use
>>> set_page_dirty() instead, as there is obviously a reference to the page
>>> existing.
>>
>> Patch [3/3] will convert above codes to use unpin_user_pages_dirty_lock()
>> which internally do the same check. So I thought to keep linux-stable and
>> linux-next code in sync. John had a similar concern [1] and later agreed to keep
>> this check.
>>
>> Shall I keep this check ? No ?
It doesn't matter *too* much, because patch 3/3 fixes up everything by
changing it all to unpin_user_pages_dirty_lock(). However, there is something
to be said for having correct interim patches, too. :) Details:
>>
>> [1] https://lore.kernel.org/xen-devel/[email protected]/
>
> I wasn't referring to checking PageDirty(), but to the use of
> set_page_dirty_lock().
>
> Looking at the comment just before the implementation of
> set_page_dirty_lock() suggests that it is fine to use set_page_dirty()
> instead (so not calling lock_page()).
no no, that's a misreading of the comment. Unless this xen/privcmd code has
somehow taken a reference on page->mapping->host (which I do *not* think is
the case), then it is still racy to call set_page_dirty() here. Instead,
set_page_dirty_lock() should be used.
>
> Only the transition from get_user_pages_fast() to pin_user_pages_fast()
> requires to use the locked version IMO.
>
That's a different misunderstanding. :) pin_user_pages*() APIs are meant to be
functionally drop-in replacements for get_user_pages*(). Internally,
pin_user_pages*() functions do some additional tracking, but from a caller's
perspective, it should look the same. In other words, there is nothing
about pin_user_pages_fast() that requires set_page_dirty_lock() upon release.
The reason set_page_dirty_lock() was chosen is that there are very few
(none at all?) call sites that need to release and dirty a page, that also meet
the requirements to safely call set_page_dirty().
That's why there is a unpin_user_pages_dirty_lock(), but there is not a
corresponding unpin_user_pages_dirty() call: the latter has not been required
so far, even though the call site conversions are nearly done.
thanks,
--
John Hubbard
NVIDIA
On 07.07.20 21:30, John Hubbard wrote:
> On 2020-07-07 04:43, Jürgen Groß wrote:
>> On 07.07.20 13:30, Souptick Joarder wrote:
>>> On Tue, Jul 7, 2020 at 3:08 PM Jürgen Groß <[email protected]> wrote:
> ...
>>>>> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
>>>>> index 33677ea..f6c1543 100644
>>>>> --- a/drivers/xen/privcmd.c
>>>>> +++ b/drivers/xen/privcmd.c
>>>>> @@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[],
>>>>> unsigned int nr_pages)
>>>>> {
>>>>> unsigned int i;
>>>>>
>>>>> - for (i = 0; i < nr_pages; i++)
>>>>> + for (i = 0; i < nr_pages; i++) {
>>>>> + if (!PageDirty(pages[i]))
>>>>> + set_page_dirty_lock(pages[i]);
>>>>
>>>> With put_page() directly following I think you should be able to use
>>>> set_page_dirty() instead, as there is obviously a reference to the page
>>>> existing.
>>>
>>> Patch [3/3] will convert above codes to use
>>> unpin_user_pages_dirty_lock()
>>> which internally do the same check. So I thought to keep linux-stable
>>> and
>>> linux-next code in sync. John had a similar concern [1] and later
>>> agreed to keep
>>> this check.
>>>
>>> Shall I keep this check ? No ?
>
> It doesn't matter *too* much, because patch 3/3 fixes up everything by
> changing it all to unpin_user_pages_dirty_lock(). However, there is
> something
> to be said for having correct interim patches, too. :) Details:
>
>>>
>>> [1]
>>> https://lore.kernel.org/xen-devel/[email protected]/
>>>
>>
>> I wasn't referring to checking PageDirty(), but to the use of
>> set_page_dirty_lock().
>>
>> Looking at the comment just before the implementation of
>> set_page_dirty_lock() suggests that it is fine to use set_page_dirty()
>> instead (so not calling lock_page()).
>
>
> no no, that's a misreading of the comment. Unless this xen/privcmd code has
> somehow taken a reference on page->mapping->host (which I do *not* think is
> the case), then it is still racy to call set_page_dirty() here. Instead,
> set_page_dirty_lock() should be used.
Ah, okay. Thanks for the clarification.
So you can add my
Reviewed-by: Juergen Gross <[email protected]>
Juergen