The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 779055842da5b2e508f3ccf9a8153cb1f704f566 Mon Sep 17 00:00:00 2001

From: Souptick Joarder jrdr.linux@gmail.com Date: Sun, 6 Sep 2020 12:21:53 +0530 Subject: [PATCH] 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 boris.ostrovsky@oracle.com Signed-off-by: Souptick Joarder jrdr.linux@gmail.com Cc: John Hubbard jhubbard@nvidia.com Cc: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: Juergen Gross jgross@suse.com Cc: David Vrabel david.vrabel@citrix.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/1599375114-32360-1-git-send-email-jrdr.linux@gmail... Reviewed-by: Boris Ostrovsky boris.ostrovsky@oracle.com Signed-off-by: Boris Ostrovsky boris.ostrovsky@oracle.com

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 64a9025a87be..1f32db7b72b2 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;