linux-kernel - Re: [PATCH v3 2/7] iommu/vt-d: Remove identity mappings from si

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Message-ID: <20240806170529.GK676757@ziepe.ca>
Date: Tue, 6 Aug 2024 14:05:29 -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 2/7] iommu/vt-d: Remove identity mappings from
 si_domain

On Tue, Aug 06, 2024 at 10:39:36AM +0800, Lu Baolu wrote:
> As the driver has enforced DMA domains for devices managed by an IOMMU
> hardware that doesn't support passthrough translation mode, there is no
> need for static identity mappings in the si_domain. Remove the identity
> mapping code to avoid dead code.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c | 122 ++----------------------------------
>  1 file changed, 4 insertions(+), 118 deletions(-)

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

I always wondered why this was so fine grained, I would have expected
it to work on blocks of 512 x 1G, once you allocate a memory for the
1G table level you may as well fill it with identity IOPTEs. The only
optimization point is how many blocks of 512x1G are needed..

Jason