From: Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>
To: Jerome Glisse <j.glisse-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: alexander.deucher-5C7GfCeVMHo@public.gmane.org,
iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
Subject: Re: IOMMU and domain binding/unbinding logic
Date: Thu, 26 Mar 2015 18:09:35 +0100 [thread overview]
Message-ID: <20150326170935.GX4441@8bytes.org> (raw)
In-Reply-To: <20150326165046.GA2965-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Hi Jerome,
On Thu, Mar 26, 2015 at 12:50:47PM -0400, Jerome Glisse wrote:
> So how comes it still looks like it is working properly ? My best guest
> it is because it is by default in passthrough, but i haven't checked that
> theory.
Your guess is correct, devices that might potentially use IOMMUv2
functionality are identity mapped by default. The reason is that IOMMU
hardware implements two dimensional paging, where the addresses in the
guest page-tables (the ones translating PASID requests) are translated
by the host page-tables. So to be able to use CPU page-tables (mm->pgd)
for the IOMMU, the host page-tables need to be identity mapped.
The other reason is, as you observed already, that host-only dma
mappings need to work in parallel.
Joerg
next prev parent reply other threads:[~2015-03-26 17:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-26 16:50 IOMMU and domain binding/unbinding logic Jerome Glisse
[not found] ` <20150326165046.GA2965-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-03-26 17:09 ` Joerg Roedel [this message]
[not found] ` <20150326170935.GX4441-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>
2015-03-26 17:58 ` Jerome Glisse
[not found] ` <20150326175857.GA3196-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-03-30 9:46 ` Joerg Roedel
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