LinuxPPC-Dev Archive on
 help / color / Atom feed
From: Ram Pai <>
To: David Gibson <>
Subject: RE: [RFC v2 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor.
Date: Mon, 11 Nov 2019 17:15:30 -0800
Message-ID: <> (raw)
In-Reply-To: <20191110194006.GQ2461@umbus.Home>

On Sun, Nov 10, 2019 at 07:40:06PM +0000, David Gibson wrote:
> On Fri, Nov 08, 2019 at 03:00:10PM -0800, Ram Pai wrote:
> > The hypervisor needs to access the contents of the page holding the TCE
> > entries while setting up the TCE entries in the IOMMU's TCE table.
> > 
> > For SecureVMs, since this page is encrypted, the hypervisor cannot
> > access valid entries. Share the page with the hypervisor. This ensures
> > that the hypervisor sees those valid entries.
> > 
> > Why is this safe?
> >    The page contains only TCE entries; not any sensitive data
> >    belonging to the Secure VM. The hypervisor has a genuine need to know
> >    the value of the TCE entries, without which it will not be able to
> >    DMA to/from the pages pointed to by the TCE entries. In a Secure
> >    VM the TCE entries point to pages that are also shared with the
> >    hypervisor; example: pages containing bounce buffers.
> The bit that may not be obvious to reviewers from the above is this:
> This is *not* a page of "live" TCEs which are actively used for
> translation.  Instead this is just a transient buffer with a batch of
> TCEs to set, passed to the hypervisor with the H_PUT_TCE_INDIRECT call.

That is true.  I should have stated that explicitly. Thanks. will
update the commit log.


      reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-08 23:00 [RFC v2 0/2] Enable IOMMU support for pseries Secure VMs Ram Pai
2019-11-08 23:00 ` [RFC v2 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Ram Pai
2019-11-08 23:00   ` [RFC v2 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs aswell Ram Pai
2019-11-10 19:40   ` [RFC v2 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor David Gibson
2019-11-12  1:15     ` Ram Pai [this message]

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LinuxPPC-Dev Archive on

Archives are clonable:
	git clone --mirror linuxppc-dev/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linuxppc-dev linuxppc-dev/ \
	public-inbox-index linuxppc-dev

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone