linux-kernel - Re: [PATCH v2 1/2] iommu/virtio: Make use of ops->iotlb_sync

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Message-ID: <42860c87-cf4d-0413-c3ae-b74ee9e7e5e6@linux.intel.com>
Date:   Mon, 25 Sep 2023 10:48:21 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, Robin Murphy <robin.murphy@....com>
Cc:     baolu.lu@...ux.intel.com,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        virtualization@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iommu/virtio: Make use of ops->iotlb_sync_map

On 9/23/23 7:33 AM, Jason Gunthorpe wrote:
> On Fri, Sep 22, 2023 at 07:07:40PM +0100, Robin Murphy wrote:
> 
>> virtio isn't setting ops->pgsize_bitmap for the sake of direct mappings
>> either; it sets it once it's discovered any instance, since apparently it's
>> assuming that all instances must support identical page sizes, and thus once
>> it's seen one it can work "normally" per the core code's assumptions. It's
>> also I think the only driver which has a "finalise" bodge but*can*  still
>> properly support map-before-attach, by virtue of having to replay mappings
>> to every new endpoint anyway.
> Well it can't quite do that since it doesn't know the geometry - it
> all is sort of guessing and hoping it doesn't explode on replay. If it
> knows the geometry it wouldn't need finalize...

The ultimate solution to this problem seems to be to add device pointer
to the parameter of ops->domain_alloc. So once the domain is allocated,
it is fully initialized. Attaching this domain to a device that is not
compatible will return -EINVAL, then the caller has to allocate a new
domain for this device.

I feel that this is not an AMD specific problem, other iommu drivers
will also encounter the similar problem sooner or later.

Best regards,
baolu