Re: [PATCH] xen/swiotlb: correct the check for xen_destroy_contiguous_region

From: Christoph Hellwig
Date: Tue Apr 28 2020 - 04:02:29 EST


On Tue, Apr 28, 2020 at 03:33:45PM +0800, peng.fan@xxxxxxx wrote:
>
> In xen_swiotlb_alloc_coherent, if !(dev_addr + size - 1 <= dma_mask) or
> range_straddles_page_boundary(phys, size) are true, it will
> create contiguous region. So when free, we need to free contiguous
> region use upper check condition.
>
> Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
> ---
> drivers/xen/swiotlb-xen.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index b6d27762c6f8..ab96e468584f 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -346,8 +346,8 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
> /* Convert the size to actually allocated. */
> size = 1UL << (order + XEN_PAGE_SHIFT);
>
> - if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
> - range_straddles_page_boundary(phys, size)) &&
> + if (((dev_addr + size - 1 > dma_mask) ||
> + range_straddles_page_boundary(phys, size)) &&
> TestClearPageXenRemapped(virt_to_page(vaddr)))

No need for the inner braces.

But more importantly please factor our a helper that can be used by
alloc and free to make sure that they always stay in sync. Something
like:

static inline bool xen_swiotlb_need_contiguous_region(struct device *dev,
phys_addr_t phys, size_t size)
{

return xen_phys_to_bus(phys) + size - 1 > dev->coherent_dma_mask ||
range_straddles_page_boundary(phys, size))
}