linux-kernel - Re: [PATCH 01/10] swiotlb-xen: use vmalloc_to

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Date:   Thu, 21 May 2020 09:01:31 +0100
From:   Julien Grall <julien@....org>
To:     Stefano Stabellini <sstabellini@...nel.org>, jgross@...e.com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano.stabellini@...inx.com>
Subject: Re: [PATCH 01/10] swiotlb-xen: use vmalloc_to_page on vmalloc virt
 addresses

Hi,

On 21/05/2020 00:45, Stefano Stabellini wrote:
> From: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> 
> Don't just assume that virt_to_page works on all virtual addresses.
> Instead add a is_vmalloc_addr check and use vmalloc_to_page on vmalloc
> virt addresses.

Can you provide an example where swiotlb is used with vmalloc()?

> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...inx.com>
> ---
>   drivers/xen/swiotlb-xen.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index b6d27762c6f8..a42129cba36e 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -335,6 +335,7 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>   	int order = get_order(size);
>   	phys_addr_t phys;
>   	u64 dma_mask = DMA_BIT_MASK(32);
> +	struct page *pg;
>   
>   	if (hwdev && hwdev->coherent_dma_mask)
>   		dma_mask = hwdev->coherent_dma_mask;
> @@ -346,9 +347,11 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>   	/* Convert the size to actually allocated. */
>   	size = 1UL << (order + XEN_PAGE_SHIFT);
>   
> +	pg = is_vmalloc_addr(vaddr) ? vmalloc_to_page(vaddr) :
> +				      virt_to_page(vaddr);

Common DMA code seems to protect this check with CONFIG_DMA_REMAP. Is it 
something we want to do it here as well? Or is there any other condition 
where vmalloc can happen?

>   	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
>   		     range_straddles_page_boundary(phys, size)) &&
> -	    TestClearPageXenRemapped(virt_to_page(vaddr)))
> +	    TestClearPageXenRemapped(pg))
>   		xen_destroy_contiguous_region(phys, order);
>   
>   	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
> 

Cheers,

-- 
Julien Grall