Re: [PATCH v7 09/13] confidential guest support: Update documentation

David Gibson
2021-01-29T05:09:38Z

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On Fri, Jan 15, 2021 at 04:36:46PM +0100, Cornelia Huck wrote:
> On Thu, 14 Jan 2021 10:58:07 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
>
> > Now that we've implemented a generic machine option for configuring various
> > confidential guest support mechanisms:
> > 1. Update docs/amd-memory-encryption.txt to reference this rather than
> > the earlier SEV specific option
> > 2. Add a docs/confidential-guest-support.txt to cover the generalities of
> > the confidential guest support scheme
> >
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> > docs/amd-memory-encryption.txt | 2 +-
> > docs/confidential-guest-support.txt | 43 +++++++++++++++++++++++++++++
> > 2 files changed, 44 insertions(+), 1 deletion(-)
> > create mode 100644 docs/confidential-guest-support.txt
> >
> > diff --git a/docs/amd-memory-encryption.txt b/docs/amd-memory-encryption.txt
> > index 80b8eb00e9..145896aec7 100644
> > --- a/docs/amd-memory-encryption.txt
> > +++ b/docs/amd-memory-encryption.txt
> > @@ -73,7 +73,7 @@ complete flow chart.
> > To launch a SEV guest
> >
> > # ${QEMU} \
> > - -machine ...,memory-encryption=sev0 \
> > + -machine ...,confidential-guest-support=sev0 \
> > -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1
> >
> > Debugging
> > diff --git a/docs/confidential-guest-support.txt b/docs/confidential-guest-support.txt
> > new file mode 100644
> > index 0000000000..2790425b38
> > --- /dev/null
> > +++ b/docs/confidential-guest-support.txt
>
> Maybe make this a proper .rst from the start and hook this up into the
> system guide? It is already almost there.

Hrm. I considered it, but didn't really want to spend the time
integrating it into the overall structure of the system guide. I kind
of want to get this dang thing wrapped up.

>
> > @@ -0,0 +1,43 @@
> > +Confidential Guest Support
> > +==========================
> > +
> > +Traditionally, hypervisors such as qemu have complete access to a
>
> s/qemu/QEMU/ ?

Fixed.

>
> > +guest's memory and other state, meaning that a compromised hypervisor
> > +can compromise any of its guests. A number of platforms have added
> > +mechanisms in hardware and/or firmware which give guests at least some
> > +protection from a compromised hypervisor. This is obviously
> > +especially desirable for public cloud environments.
> > +
> > +These mechanisms have different names and different modes of
> > +operation, but are often referred to as Secure Guests or Confidential
> > +Guests. We use the term "Confidential Guest Support" to distinguish
> > +this from other aspects of guest security (such as security against
> > +attacks from other guests, or from network sources).
> > +
> > +Running a Confidential Guest
> > +----------------------------
> > +
> > +To run a confidential guest you need to add two command line parameters:
> > +
> > +1. Use "-object" to create a "confidential guest support" object. The
> > + type and parameters will vary with the specific mechanism to be
> > + used
> > +2. Set the "confidential-guest-support" machine parameter to the ID of
> > + the object from (1).
> > +
> > +Example (for AMD SEV)::
> > +
> > + qemu-system-x86_64 \
> > + <other parameters> \
> > + -machine ...,confidential-guest-support=sev0 \
> > + -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1
> > +
> > +Supported mechanisms
> > +--------------------
> > +
> > +Currently supported confidential guest mechanisms are:
> > +
> > +AMD Secure Encrypted Virtualization (SEV)
> > + docs/amd-memory-encryption.txt
> > +
> > +Other mechanisms may be supported in future.
>
> LGTM.
>

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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