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

[Cornelia Huck]

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.

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

s/qemu/QEMU/ ?

> +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.