Re: [Xen-devel] [PATCH v2 3/3] xen/swiotlb: remember having called xen_create_contiguous_region()

[Jan Beulich]

>>> On 29.05.19 at 11:04, <jgross@xxxxxxxx> wrote:
> @@ -345,8 +346,11 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>  	size = 1UL << (order + XEN_PAGE_SHIFT);
>  
>  	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
> -		     range_straddles_page_boundary(phys, size)))
> +		     range_straddles_page_boundary(phys, size)) &&
> +	    PageXenRemapped(virt_to_page(vaddr))) {
>  		xen_destroy_contiguous_region(phys, order);
> +		ClearPageXenRemapped(virt_to_page(vaddr));
> +	}

To be symmetric with setting the flag only after having made the region
contiguous, and to avoid (perhaps just theoretical) races, wouldn't it be
better to clear the flag before calling xen_destroy_contiguous_region()?
Even better would be a TestAndClear...() operation.

Jan