Re: [PATCH v2 15/30] iommu/mtk_v1: implement iova_to_phys_length

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Valid PTE mappings to physical address 0 are incorrectly treated as unmapped.
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commit 8a65585ea3e0470504b1a4dc830dd977b11466cf
Author: Guanghui Feng <guanghuifeng@linux.alibaba.com>

iommu/mtk_v1: implement iova_to_phys_length
    
This commit implements the iova_to_phys_length callback for the MediaTek
v1 IOMMU driver to return the actual PTE mapping size. It also fixes a
bug by adding the page offset to the physical address.

> diff --git a/drivers/iommu/mtk_iommu_v1.c b/drivers/iommu/mtk_iommu_v1.c
> --- a/drivers/iommu/mtk_iommu_v1.c
> +++ b/drivers/iommu/mtk_iommu_v1.c
[ ... ]
> -static phys_addr_t mtk_iommu_v1_iova_to_phys(struct iommu_domain *domain, dma_addr_t iova)
> +static phys_addr_t mtk_iommu_v1_iova_to_phys_length(struct iommu_domain *domain,
> +						    dma_addr_t iova,
> +						    size_t *mapped_length)
>  {
>  	struct mtk_iommu_v1_domain *dom = to_mtk_domain(domain);
>  	unsigned long flags;
>  	phys_addr_t pa;
>  
> +	if (mapped_length)
> +		*mapped_length = 0;
> +
>  	spin_lock_irqsave(&dom->pgtlock, flags);
>  	pa = *(dom->pgt_va + (iova >> MT2701_IOMMU_PAGE_SHIFT));
>  	pa = pa & (~(MT2701_IOMMU_PAGE_SIZE - 1));
>  	spin_unlock_irqrestore(&dom->pgtlock, flags);
>  
> +	if (!pa)
> +		return PHYS_ADDR_MAX;

[Severity: High]
Does this incorrectly treat a valid mapping at physical address 0 as
unmapped?

If the hardware PTE points to physical address 0x0, the raw PTE contains
valid flags, but the masking operation isolates just the physical address:

    pa = pa & (~(MT2701_IOMMU_PAGE_SIZE - 1));

This results in pa evaluating to 0. The subsequent if (!pa) check will
then evaluate to true, returning PHYS_ADDR_MAX and leaving mapped_length
as 0.

Should this code check the valid bit on the raw PTE before applying the
physical address mask to determine if the page is mapped?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260602104637.1219810-1-guanghuifeng@linux.alibaba.com?part=15