linux-kernel - Re: [PATCH] dma-mapping: reliably inform about DMA support for IOMMU

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20240912105009.GI4026@unreal>
Date: Thu, 12 Sep 2024 13:50:09 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Nícolas F. R. A. Prado <nfraprado@...labora.com>
Subject: Re: [PATCH] dma-mapping: reliably inform about DMA support for IOMMU

On Thu, Sep 12, 2024 at 09:29:54AM +0200, Christoph Hellwig wrote:
> Thanks, I've applied this.  I do like the flow of dma_supported even
> less with the duplicate condition now.  Can I get a quick review for
> this incremental cleanup, please?
> 
> ---
> From d311bfe189d12a836b4add55fdb946f37f8697fa Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@....de>
> Date: Thu, 12 Sep 2024 09:21:18 +0200
> Subject: dma-mapping: reflow dma_supported
> 
> dma_supported has become too much spaghetti for my taste.  Reflow it to
> remove the duplicate use_dma_iommu condition and make the main path more
> obvious.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  kernel/dma/mapping.c | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)

Reviewed-by: Leon Romanovsky <leon@...nel.org>

> 
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 022d670f8cad29..cd2a97d362cd24 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -841,20 +841,23 @@ static int dma_supported(struct device *dev, u64 mask)
>  {
>  	const struct dma_map_ops *ops = get_dma_ops(dev);
>  
> -	if (WARN_ON(ops && use_dma_iommu(dev)))
> -		return false;
> -
> -	if (use_dma_iommu(dev))
> +	if (use_dma_iommu(dev)) {
> +		if (WARN_ON(ops))
> +			return false;
>  		return true;

You can write it as "return !WARN_ON(ops);" if you want to be fancy, but
your version is perfectly fine too, so ignore this comment :).

> +	}
> +
>  	/*
> -	 * ->dma_supported sets the bypass flag, so we must always call
> -	 * into the method here unless the device is truly direct mapped.
> +	 * ->dma_supported sets and clears the bypass flag, so ignore it here
> +	 * and always call into the method if there is one.
>  	 */
> -	if (!ops)
> -		return dma_direct_supported(dev, mask);
> -	if (!ops->dma_supported)
> -		return 1;
> -	return ops->dma_supported(dev, mask);
> +	if (ops) {
> +		if (!ops->dma_supported)
> +			return 1;

Worth to change it to be "return true;"

> +		return ops->dma_supported(dev, mask);
> +	}
> +
> +	return dma_direct_supported(dev, mask);
>  }
>  
>  bool dma_pci_p2pdma_supported(struct device *dev)
> -- 
> 2.45.2
>