linux-kernel - Re: [PATCH 6/7] iommu/vt-d: Refactor first_level_by

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Message-ID: <20241011163123.GO762027@ziepe.ca>
Date: Fri, 11 Oct 2024 13:31:23 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: iommu@...ts.linux.dev, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
	Vasant Hegde <vasant.hegde@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] iommu/vt-d: Refactor first_level_by_default()

On Fri, Oct 11, 2024 at 12:27:21PM +0800, Lu Baolu wrote:
> The first stage page table is compatible across host and guest kernels.
> Therefore, this driver uses the first stage page table as the default for
> paging domains.
> 
> The helper first_level_by_default() determines the feasibility of using
> the first stage page table based on a global policy. This policy requires
> consistency in scalable mode and first stage translation capability among
> all iommu units. However, this is unnecessary as domain allocation,
> attachment, and removal operations are performed on a per-device basis.
> 
> The domain type (IOMMU_DOMAIN_DMA vs. IOMMU_DOMAIN_UNMANAGED) should not
> be a factor in determining the first stage page table usage. Both types
> are for paging domains, and there's no fundamental difference between them.
> The driver should not be aware of this distinction unless the core
> specifies allocation flags that require special handling.
> 
> Convert first_level_by_default() from global to per-iommu and remove the
> 'type' input.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason