2020-09-06 06:58:21

by Souptick Joarder

Subject: [PATCH 1/2] xen/gntdev.c: Mark pages as dirty

There seems to be a bug in the original code when gntdev_get_page()
is called with writeable=true then the page needs to be marked dirty
before being put.

To address this, a bool writeable is added in gnt_dev_copy_batch, set
it in gntdev_grant_copy_seg() (and drop `writeable` argument to
gntdev_get_page()) and then, based on batch->writeable, use
set_page_dirty_lock().

Fixes: a4cdb556cae0 (xen/gntdev: add ioctl for grant copy)
Suggested-by: Boris Ostrovsky <[email protected]>
Signed-off-by: Souptick Joarder <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: David Vrabel <[email protected]>
---
drivers/xen/gntdev.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 64a9025a..5e1411b 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -720,17 +720,18 @@ struct gntdev_copy_batch {
s16 __user *status[GNTDEV_COPY_BATCH];
unsigned int nr_ops;
unsigned int nr_pages;
+ bool writeable;
};

static int gntdev_get_page(struct gntdev_copy_batch *batch, void __user *virt,
- bool writeable, unsigned long *gfn)
+ unsigned long *gfn)
{
unsigned long addr = (unsigned long)virt;
struct page *page;
unsigned long xen_pfn;
int ret;

- ret = get_user_pages_fast(addr, 1, writeable ? FOLL_WRITE : 0, &page);
+ ret = get_user_pages_fast(addr, 1, batch->writeable ? FOLL_WRITE : 0, &page);
if (ret < 0)
return ret;

@@ -746,9 +747,13 @@ static void gntdev_put_pages(struct gntdev_copy_batch *batch)
{
unsigned int i;

- for (i = 0; i < batch->nr_pages; i++)
+ for (i = 0; i < batch->nr_pages; i++) {
+ if (batch->writeable && !PageDirty(batch->pages[i]))
+ set_page_dirty_lock(batch->pages[i]);
put_page(batch->pages[i]);
+ }
batch->nr_pages = 0;
+ batch->writeable = false;
}

static int gntdev_copy(struct gntdev_copy_batch *batch)
@@ -837,8 +842,9 @@ static int gntdev_grant_copy_seg(struct gntdev_copy_batch *batch,
virt = seg->source.virt + copied;
off = (unsigned long)virt & ~XEN_PAGE_MASK;
len = min(len, (size_t)XEN_PAGE_SIZE - off);
+ batch->writeable = false;

- ret = gntdev_get_page(batch, virt, false, &gfn);
+ ret = gntdev_get_page(batch, virt, &gfn);
if (ret < 0)
return ret;

@@ -856,8 +862,9 @@ static int gntdev_grant_copy_seg(struct gntdev_copy_batch *batch,
virt = seg->dest.virt + copied;
off = (unsigned long)virt & ~XEN_PAGE_MASK;
len = min(len, (size_t)XEN_PAGE_SIZE - off);
+ batch->writeable = true;

- ret = gntdev_get_page(batch, virt, true, &gfn);
+ ret = gntdev_get_page(batch, virt, &gfn);
if (ret < 0)
return ret;

--
1.9.1

2020-09-11 19:54:36

by Boris Ostrovsky

Subject: Re: [PATCH 1/2] xen/gntdev.c: Mark pages as dirty

On 9/6/20 2:51 AM, Souptick Joarder wrote:
> There seems to be a bug in the original code when gntdev_get_page()
> is called with writeable=true then the page needs to be marked dirty
> before being put.
>
> To address this, a bool writeable is added in gnt_dev_copy_batch, set
> it in gntdev_grant_copy_seg() (and drop `writeable` argument to
> gntdev_get_page()) and then, based on batch->writeable, use
> set_page_dirty_lock().
>
> Fixes: a4cdb556cae0 (xen/gntdev: add ioctl for grant copy)
> Suggested-by: Boris Ostrovsky <[email protected]>
> Signed-off-by: Souptick Joarder <[email protected]>
> Cc: John Hubbard <[email protected]>
> Cc: Boris Ostrovsky <[email protected]>
> Cc: Juergen Gross <[email protected]>
> Cc: David Vrabel <[email protected]>


Cc: [email protected]

(can be added at commit time)

Reviewed-by: Boris Ostrovsky <[email protected]>