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Date:   Sat, 21 Oct 2023 13:39:07 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Baolu Lu <baolu.lu@linux.intel.com>
Cc:     Nicolin Chen <nicolinc@nvidia.com>, kevin.tian@intel.com,
        joro@8bytes.org, will@kernel.org, robin.murphy@arm.com,
        iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
        yi.l.liu@intel.com
Subject: Re: [PATCH 0/2] iommufd: Only enforce_cache_coherency when
 allocating hwpt
Message-ID: <20231021163907.GM3952@nvidia.com>
References: <cover.1697848510.git.nicolinc@nvidia.com>
 <2201ae4d-b825-49a5-ba73-c6b310e2969c@linux.intel.com>
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On Sat, Oct 21, 2023 at 09:32:32AM +0800, Baolu Lu wrote:
> On 2023/10/21 8:37, Nicolin Chen wrote:
> > https://lore.kernel.org/linux-iommu/20231020135501.GG3952@nvidia.com/
> > The conversation above concluded that a hwpt should only enforce cache
> > coherency per device at the stage of its allocation, and it should not
> > be changed or updated in the attach/replace routines.
> > 
> > Add two patches dropping the enforce_cache_coherency calls from attach
> > and replce routines respectively, since they were introduced with two
> > different commits.
> > 
> > Nicolin Chen (2):
> >    iommufd/device: Drop enforce_cache_coherency in
> >      iommufd_device_do_replace
> >    iommufd/device: Drop enforce_cache_coherency in
> >      iommufd_hw_pagetable_attach
> > 
> >   drivers/iommu/iommufd/device.c          | 19 ++-----------------
> >   drivers/iommu/iommufd/hw_pagetable.c    |  2 +-
> >   drivers/iommu/iommufd/iommufd_private.h |  1 -
> >   3 files changed, 3 insertions(+), 19 deletions(-)
> 
> Hi Kevin and Jason,
> 
> With these two fixes, there's no issue in the intel driver any more. Do
> I understand it right?

I think so, as long as it is an allocation only time flag there isn't
much trouble for the driver.

VFIO, I think, still does the old algorithm however.

Jason