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

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Message-ID: <3af0ac5a-ec1b-464b-bacc-29d2aa491a79@linux.intel.com>
Date: Wed, 7 Aug 2024 14:14:11 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, 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 2024/8/7 1:05, Jason Gunthorpe wrote:
> 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..

I am not sure whether or not those early hardware support super pages.
  :-).

Thanks,
baolu