linux-kernel - Re: [PATCH v1] iommu/vt-d: Remove dead code in intel_iommu_domain_alloc_paging

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Message-ID: <f1f55968-28e0-4c5d-876b-1c5499b3c01a@linux.intel.com>
Date: Tue, 3 Jun 2025 10:39:51 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Wei Wang <wei.w.wang@...el.com>, kevin.tian@...el.com,
 yi.l.liu@...el.com, dwmw2@...radead.org, jroedel@...e.de,
 linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Subject: Re: [PATCH v1] iommu/vt-d: Remove dead code in
 intel_iommu_domain_alloc_paging_flags()

On 5/30/25 17:13, Wei Wang wrote:
> When dirty_tracking is enabled, first_stage is set to false to use the
> second stage translation table. dmar_domain->use_first_level, which is
> assigned from first_page, is guaranteed to be false when the execution
> reaches the location of the code to be removed by this patch. So the
> handling for dmar_domain->use_first_level being true there will never
> be executed.
> 
> Signed-off-by: Wei Wang<wei.w.wang@...el.com>
> ---
>   drivers/iommu/intel/iommu.c | 7 +------
>   1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index cb0b993bebb4..1145567c60f9 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -3418,13 +3418,8 @@ intel_iommu_domain_alloc_paging_flags(struct device *dev, u32 flags,
>   		spin_lock_init(&dmar_domain->s1_lock);
>   	}
>   
> -	if (dirty_tracking) {
> -		if (dmar_domain->use_first_level) {

This *explicit* check enforces that dirty tracking cannot be supported
for a domain that relies on first-stage translation due to the lack of
enabling/disabling dirty tracking support.

While this might appear redundant, this prevents potential issues
if related code is modified without awareness of this dependency.

> -			iommu_domain_free(domain);
> -			return ERR_PTR(-EOPNOTSUPP);
> -		}

Thanks,
baolu