linux-kernel - Re: [PATCH v2 2/2] xen/swiotlb: fix allocated size

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Message-ID: <d0075562-6a21-4a87-b7f5-854f09c0743a@suse.com>
Date: Mon, 16 Sep 2024 09:59:59 +0200
From: Jan Beulich <jbeulich@...e.com>
To: Juergen Gross <jgross@...e.com>
Cc: Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
 iommu@...ts.linux.dev
Subject: Re: [PATCH v2 2/2] xen/swiotlb: fix allocated size

On 16.09.2024 08:47, Juergen Gross wrote:
> The allocated size in xen_swiotlb_alloc_coherent() and
> xen_swiotlb_free_coherent() is calculated wrong for the case of
> XEN_PAGE_SIZE not matching PAGE_SIZE. Fix that.
> 
> Fixes: 7250f422da04 ("xen-swiotlb: use actually allocated size on check physical continuous")
> Reported-by: Jan Beulich <jbeulich@...e.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>

Reviewed-by: Jan Beulich <jbeulich@...e.com>

> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -147,7 +147,7 @@ xen_swiotlb_alloc_coherent(struct device *dev, size_t size,
>  	void *ret;
>  
>  	/* Align the allocation to the Xen page size */
> -	size = 1UL << (order + XEN_PAGE_SHIFT);
> +	size = ALIGN(size, XEN_PAGE_SIZE);

The way you're doing it has further positive effects, as the size
is now also no longer needlessly over-aligned. May want mentioning
in the description. Hope of course is that no-one came to rely on
the up-to-next-power-of-2 allocation anywhere (which of course
would be a bug there, yet might end in a perceived regression).

Jan