[RFC PATCH v2 0/3] mm/gup: introduce vaddr_pin_pages_remote(), FOLL_PIN

[RFC PATCH v2 0/3] mm/gup: introduce vaddr_pin_pages_remote(), FOLL_PIN

[jhubbard]

From: John Hubbard <jhubbard@nvidia.com>

Hi Ira,

As requested, this is for your tree:
https://github.com/weiny2/linux-kernel.git (mmotm-rdmafsdax-b0-v4), to be
applied at your last authored commit, which is: commit f625f92ecfb4
("mm/gup: Remove FOLL_LONGTERM DAX exclusion"). In other words, please
delete my previous patches from the tree, and apply these replacement
patches.

This now has a user for the new vaddr_pin_user_pages_remote() call. And
it also moves the gup flag setting out to the caller.

I'm pretty pleased to be able to include a bit of documentation (see the
FOLL_PIN patch) that covers those four cases. This should really help
clarify things. Thanks to Jan Kara and Vlastimil Babka for providing
the meaingful core of that documentation.

The naming can of course be tweaked to match whatever the final is. For
now, I've used vaddr_pin_user_pages_remote(). That addresses Jason's
request for a "user" in the name, and it also makes it very clear that
it's a replacement for get_user_pages_remote().

v1 of this RFC is here:
https://lore.kernel.org/r/20190812015044.26176-1-jhubbard@nvidia.com

John Hubbard (3):
  For Ira: tiny formatting tweak to kerneldoc
  mm/gup: introduce FOLL_PIN flag for get_user_pages()
  mm/gup: introduce vaddr_pin_pages_remote(), and invoke it

 include/linux/mm.h     | 61 +++++++++++++++++++++++++++++++++++++-----
 mm/gup.c               | 37 +++++++++++++++++++++++--
 mm/process_vm_access.c | 23 +++++++++-------
 3 files changed, 104 insertions(+), 17 deletions(-)

-- 
2.22.1

[RFC PATCH v2 1/3] For Ira: tiny formatting tweak to kerneldoc

[jhubbard]

From: John Hubbard <jhubbard@nvidia.com>

For your vaddr_pin_pages() and vaddr_unpin_pages().
Just merge it into wherever it goes please. Didn't want to
cause merge problems so it's a separate patch-let.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 56421b880325..e49096d012ea 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2465,7 +2465,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 EXPORT_SYMBOL_GPL(get_user_pages_fast);
 
 /**
- * vaddr_pin_pages pin pages by virtual address and return the pages to the
+ * vaddr_pin_pages() - pin pages by virtual address and return the pages to the
  * user.
  *
  * @addr: start address
@@ -2505,7 +2505,7 @@ long vaddr_pin_pages(unsigned long addr, unsigned long nr_pages,
 EXPORT_SYMBOL(vaddr_pin_pages);
 
 /**
- * vaddr_unpin_pages - counterpart to vaddr_pin_pages
+ * vaddr_unpin_pages() - counterpart to vaddr_pin_pages
  *
  * @pages: array of pages returned
  * @nr_pages: number of pages in pages
-- 
2.22.1

[RFC PATCH v2 2/3] mm/gup: introduce FOLL_PIN flag for get_user_pages()

[jhubbard]

From: John Hubbard <jhubbard@nvidia.com>
DKIM-Signature: v\x01 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[RFC PATCH v2 3/3] mm/gup: introduce vaddr_pin_pages_remote(), and invoke it

[jhubbard]

From: John Hubbard <jhubbard@nvidia.com>

vaddr_pin_user_pages_remote() is the "vaddr_pin_pages" corresponding
variant to get_user_pages_remote(): it adds the ability to handle
FOLL_PIN, FOLL_LONGTERM, or both.

Note that the put_user_page*() requirement won't be truly required until
all of the call sites have been converted, and the tracking of pages is
activated.

Also, change process_vm_rw_single_vec() to invoke the new function.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h     |  5 +++++
 mm/gup.c               | 33 +++++++++++++++++++++++++++++++++
 mm/process_vm_access.c | 23 ++++++++++++++---------
 3 files changed, 52 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6e7de424bf5e..849b509e9f89 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1606,6 +1606,11 @@ int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
 long vaddr_pin_pages(unsigned long addr, unsigned long nr_pages,
 		     unsigned int gup_flags, struct page **pages,
 		     struct vaddr_pin *vaddr_pin);
+long vaddr_pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
+				 unsigned long start, unsigned long nr_pages,
+				 unsigned int gup_flags, struct page **pages,
+				 struct vm_area_struct **vmas, int *locked,
+				 struct vaddr_pin *vaddr_pin);
 void vaddr_unpin_pages(struct page **pages, unsigned long nr_pages,
 		       struct vaddr_pin *vaddr_pin, bool make_dirty);
 bool mapping_inode_has_layout(struct vaddr_pin *vaddr_pin, struct page *page);
diff --git a/mm/gup.c b/mm/gup.c
index e49096d012ea..d7ce9b38178f 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2522,3 +2522,36 @@ void vaddr_unpin_pages(struct page **pages, unsigned long nr_pages,
 	__put_user_pages_dirty_lock(pages, nr_pages, make_dirty, vaddr_pin);
 }
 EXPORT_SYMBOL(vaddr_unpin_pages);
+
+/**
+ * vaddr_pin_user_pages_remote() - pin pages by virtual address and return the
+ * pages to the user.
+ *
+ * @tsk:	the task_struct to use for page fault accounting, or
+ *		NULL if faults are not to be recorded.
+ * @mm:		mm_struct of target mm
+ * @addr:	start address
+ * @nr_pages:	number of pages to pin
+ * @gup_flags:	flags to use for the pin. Please see FOLL_* documentation in
+ *		mm.h.
+ * @pages:	array of pages returned
+ * @vaddr_pin:  If FOLL_LONGTERM is set, then vaddr_pin should point to an
+ * initialized struct that contains the owning mm and file. Otherwise, vaddr_pin
+ * should be set to NULL.
+ *
+ * This is the "vaddr_pin_pages" corresponding variant to
+ * get_user_pages_remote(), but with the ability to handle FOLL_PIN,
+ * FOLL_LONGTERM, or both.
+ */
+long vaddr_pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
+				 unsigned long start, unsigned long nr_pages,
+				 unsigned int gup_flags, struct page **pages,
+				 struct vm_area_struct **vmas, int *locked,
+				 struct vaddr_pin *vaddr_pin)
+{
+	gup_flags |= FOLL_TOUCH | FOLL_REMOTE;
+
+	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
+				       locked, gup_flags, vaddr_pin);
+}
+EXPORT_SYMBOL(vaddr_pin_user_pages_remote);
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 357aa7bef6c0..e08c1f760ad4 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -96,7 +96,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
 		flags |= FOLL_WRITE;
 
 	while (!rc && nr_pages && iov_iter_count(iter)) {
-		int pages = min(nr_pages, max_pages_per_loop);
+		int pinned_pages = min(nr_pages, max_pages_per_loop);
 		int locked = 1;
 		size_t bytes;
 
@@ -106,14 +106,18 @@ static int process_vm_rw_single_vec(unsigned long addr,
 		 * current/current->mm
 		 */
 		down_read(&mm->mmap_sem);
-		pages = get_user_pages_remote(task, mm, pa, pages, flags,
-					      process_pages, NULL, &locked);
+
+		flags |= FOLL_PIN;
+		pinned_pages = vaddr_pin_user_pages_remote(task, mm, pa,
+							   pinned_pages, flags,
+							   process_pages, NULL,
+							   &locked, NULL);
 		if (locked)
 			up_read(&mm->mmap_sem);
-		if (pages <= 0)
+		if (pinned_pages <= 0)
 			return -EFAULT;
 
-		bytes = pages * PAGE_SIZE - start_offset;
+		bytes = pinned_pages * PAGE_SIZE - start_offset;
 		if (bytes > len)
 			bytes = len;
 
@@ -122,10 +126,11 @@ static int process_vm_rw_single_vec(unsigned long addr,
 					 vm_write);
 		len -= bytes;
 		start_offset = 0;
-		nr_pages -= pages;
-		pa += pages * PAGE_SIZE;
-		while (pages)
-			put_page(process_pages[--pages]);
+		nr_pages -= pinned_pages;
+		pa += pinned_pages * PAGE_SIZE;
+
+		/* If vm_write is set, the pages need to be made dirty: */
+		vaddr_unpin_pages(process_pages, pinned_pages, NULL, vm_write);
 	}
 
 	return rc;
-- 
2.22.1

Re: [RFC PATCH v2 2/3] mm/gup: introduce FOLL_PIN flag for get_user_pages()

[John Hubbard]

On 8/16/19 7:24 PM, jhubbard@nvidia.com wrote:
> From: John Hubbard <jhubbard@nvidia.com>
> DKIM-Signature: v\x01 a a-sha256; c\x0elaxed/relaxed; d idia.com; s\x01;
> 	t\x1566008674; bh\x05Mai0va6k/z2enpQJ4Nfvbj5WByFxGAO1JwdIBbXio	h PGP-Universal:From:To:CC:Subject:Date:Message-ID:X-Mailer:
> 	 In-Reply-To:References:MIME-Version:X-NVConfidentiality:
> 	 Content-Transfer-Encoding:Content-Type;
> 	bÖUDSde9XF/IsNteBaYOBWeKiHhWmeU9ekUJNvCviHssBDCtw0T+M/2TlEPEzomIT
> 	 fGXzIQNlGN6MXFbaBoyBmF/zjCu02TmTNExbVJ3/5N6PTyOuJFCx9ZN1/5gXsB11m1
> 	 xAHIWE+VOZs4qqDeHDBqKZq+FaxQHNvGz0j6lyVBA70TfseNoZqZZrSil8uvaKJwKd
> 	 TQ1ht+AGWbw9p610JmaPb4u6o/eV6Ns8Sl3EVnjWWu94T6ISNIaWCiC6wQQF6L1YCH
> 	 G5Pjn+0rEjhk6XG4TyLudi5lWp3IVBHd8+WlWlnl+bvLCC55RUAjPJLn7LaVyVdh0F
> 	 nLHwm3bN2Jotg

I cannot readily explain the above email glitch, but I did just now switch
back to mailgw.nvidia.com for this patchset, in order to get the nice behavior
of having "From:" really be my native NVIDIA email address. That's very nice,
but if the glitches happen again, I'll switch back to using gmail for 
git-send-email.

Sorry about the weirdness. It does still let you apply the patch, I
just now checked on that.

thanks,
-- 
John Hubbard
NVIDIA

Re: [RFC PATCH v2 2/3] mm/gup: introduce FOLL_PIN flag for get_user_pages()

[John Hubbard]

On 8/16/19 7:36 PM, John Hubbard wrote:
> On 8/16/19 7:24 PM, jhubbard@nvidia.com wrote:
>> From: John Hubbard <jhubbard@nvidia.com>
>> DKIM-Signature: v\x01 a a-sha256; c\x0elaxed/relaxed; d idia.com; s\x01;
>> 	t\x1566008674; bh\x05Mai0va6k/z2enpQJ4Nfvbj5WByFxGAO1JwdIBbXio	h PGP-Universal:From:To:CC:Subject:Date:Message-ID:X-Mailer:
>> 	 In-Reply-To:References:MIME-Version:X-NVConfidentiality:
>> 	 Content-Transfer-Encoding:Content-Type;
>> 	bÖUDSde9XF/IsNteBaYOBWeKiHhWmeU9ekUJNvCviHssBDCtw0T+M/2TlEPEzomIT
>> 	 fGXzIQNlGN6MXFbaBoyBmF/zjCu02TmTNExbVJ3/5N6PTyOuJFCx9ZN1/5gXsB11m1
>> 	 xAHIWE+VOZs4qqDeHDBqKZq+FaxQHNvGz0j6lyVBA70TfseNoZqZZrSil8uvaKJwKd
>> 	 TQ1ht+AGWbw9p610JmaPb4u6o/eV6Ns8Sl3EVnjWWu94T6ISNIaWCiC6wQQF6L1YCH
>> 	 G5Pjn+0rEjhk6XG4TyLudi5lWp3IVBHd8+WlWlnl+bvLCC55RUAjPJLn7LaVyVdh0F
>> 	 nLHwm3bN2Jotg
> 
> I cannot readily explain the above email glitch, but I did just now switch
> back to mailgw.nvidia.com for this patchset, in order to get the nice behavior
> of having "From:" really be my native NVIDIA email address. That's very nice,
> but if the glitches happen again, I'll switch back to using gmail for
> git-send-email.
> 
> Sorry about the weirdness. It does still let you apply the patch, I
> just now checked on that.
> 

Hi Ira, could you please let me know if you'd like me to repost this patch, or
the entire patchset, or if you're able to deal with it as-is? As it stands, the
DKIM-Signature cruft above needs to be manually removed, either from the patch, or
from the commit log after applying the patch.

Also, as noted in the email thread involving Bharath and sgi-gru [1], I'm
currently planning on branching from your tree, and continuing the misc
call site conversions from there. And then just adapting to whatever API
changes are made to vaddr_*() functions. And the biovec call site conversions should
be based on that as well.

[1] https://lore.kernel.org/r/0c2ad29b-934c-ec30-66c3-b153baf1fba5@nvidia.com

thanks,
-- 
John Hubbard
NVIDIA