linux-kernel - Re: [PATCH v3 4/7] iommu/vt-d: Prepare for global static identity domain

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Message-ID: <20240806171236.GM676757@ziepe.ca>
Date: Tue, 6 Aug 2024 14:12:36 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/7] iommu/vt-d: Prepare for global static identity
 domain

On Tue, Aug 06, 2024 at 10:39:38AM +0800, Lu Baolu wrote:
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index c019fb3b3e78..f37c8c3cba3c 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1270,6 +1270,9 @@ void domain_update_iotlb(struct dmar_domain *domain)
>  	bool has_iotlb_device = false;
>  	unsigned long flags;
>  
> +	if (!domain)
> +		return;
> +

This seems really strange, maybe wrong..

The only callers that could take advantage are
iommu_enable_pci_caps()/iommu_disable_pci_caps()

But if they are mucking with ATS then the ATC flushes should not be
done wrong!

So I looked at this and, uh, who even reads domain->has_iotlb_device ?

So I'd just delete  domain->has_iotlb_device and domain_update_iotlb()
as well.

Jason