linux-kernel - Re: [PATCH] iommu: Up front sanity check in the arm_lpae

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Message-ID: <20201207105900.GB4198@willie-the-truck>
Date:   Mon, 7 Dec 2020 10:59:01 +0000
From:   Will Deacon <will@...nel.org>
To:     Keqian Zhu <zhukeqian1@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, Marc Zyngier <maz@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        wanghaibin.wang@...wei.com, jiangkunkun@...wei.com
Subject: Re: [PATCH] iommu: Up front sanity check in the arm_lpae_map

On Sat, Dec 05, 2020 at 04:29:57PM +0800, Keqian Zhu wrote:
> ... then we have more chance to detect wrong code logic.

This could do with being a bit more explicit. Something like:

	Although handling a mapping request with no permissions is a
	trivial no-op, defer the early return until after the size/range
	checks so that we are consistent with other mapping requests.

> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
> ---
>  drivers/iommu/io-pgtable-arm.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index a7a9bc08dcd1..8ade72adab31 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -444,10 +444,6 @@ static int arm_lpae_map(struct io_pgtable_ops *ops, unsigned long iova,
>  	arm_lpae_iopte prot;
>  	long iaext = (s64)iova >> cfg->ias;
>  
> -	/* If no access, then nothing to do */
> -	if (!(iommu_prot & (IOMMU_READ | IOMMU_WRITE)))
> -		return 0;
> -
>  	if (WARN_ON(!size || (size & cfg->pgsize_bitmap) != size))
>  		return -EINVAL;
>  
> @@ -456,6 +452,10 @@ static int arm_lpae_map(struct io_pgtable_ops *ops, unsigned long iova,
>  	if (WARN_ON(iaext || paddr >> cfg->oas))
>  		return -ERANGE;
>  
> +	/* If no access, then nothing to do */
> +	if (!(iommu_prot & (IOMMU_READ | IOMMU_WRITE)))
> +		return 0;

This looks sensible to me, but please can you make the same change for
io-pgtable-arm-v7s.c so that the behaviour is consistent across the two
formats?

Thanks,

Will