Subject: Re: [RFC PATCH v8 04/14] swiotlb: Map the buffer if it was unmapped by XPFO

From: Christoph Hellwig <[email-masked]>
Date: Thu, 14 Feb 2019 08:47:47 +0100

On Wed, Feb 13, 2019 at 05:01:27PM -0700, Khalid Aziz wrote:
> +++ b/kernel/dma/swiotlb.c
> @@ -396,8 +396,9 @@ static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr,
>  {
>  	unsigned long pfn = PFN_DOWN(orig_addr);
>  	unsigned char *vaddr = phys_to_virt(tlb_addr);
> +	struct page *page = pfn_to_page(pfn);
>  
> -	if (PageHighMem(pfn_to_page(pfn))) {
> +	if (PageHighMem(page) || xpfo_page_is_unmapped(page)) {

I think this just wants a page_unmapped or similar helper instead of
needing the xpfo_page_is_unmapped check.  We actually have quite
a few similar construct in the arch dma mapping code for architectures
that require cache flushing.

> +bool xpfo_page_is_unmapped(struct page *page)
> +{
> +	struct xpfo *xpfo;
> +
> +	if (!static_branch_unlikely(&xpfo_inited))
> +		return false;
> +
> +	xpfo = lookup_xpfo(page);
> +	if (unlikely(!xpfo) && !xpfo->inited)
> +		return false;
> +
> +	return test_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags);
> +}
> +EXPORT_SYMBOL(xpfo_page_is_unmapped);

And at least for swiotlb there is no need to export this helper,
as it is always built in.

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