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    Subject[PATCH 5.9 71/74] xen/gntdev.c: Mark pages as dirty
    Date
    From: Souptick Joarder <jrdr.linux@gmail.com>

    commit 779055842da5b2e508f3ccf9a8153cb1f704f566 upstream.

    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.com
    Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/xen/gntdev.c | 17 ++++++++++++-----
    1 file changed, 12 insertions(+), 5 deletions(-)

    --- 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 gntd
    {
    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
    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
    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;


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