Messages in this thread | | | Date | Wed, 14 Jul 2021 12:25:31 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH] iommu/amd: Enable swiotlb if any device supports iommu v2 and uses identity mapping |
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On Tue, Jul 13, 2021 at 07:57:40PM -0400, Konrad Rzeszutek Wilk wrote: > The SWIOTLB does have support to do late initialization (xen-pcifront > does that for example - so if you add devices that can't do 64-bit it > will allocate something like 4MB).
That sounds like a way to evaluate. I suggest to allocate the SWIOTLB memory at boot and when the IOMMUs are initialized we re-evaluate what we ended up with and free the SWIOTLB memory if its not needed.
If that turns out to be wrong during runtime (e.g. because a device is switched to a passthrough default domain at runtime), we allocate a small aperture for this device like the above mentioned 4MB.
(A boot option to always keep the aperture around might also be helpful for some setups)
Regards,
Joerg
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