Re: [PATCH Part1 v5 07/38] x86/sev: Add support for hypervisor feature VMGEXIT

[Brijesh Singh]

On 8/23/21 4:47 AM, Borislav Petkov wrote:
> On Fri, Aug 20, 2021 at 10:19:02AM -0500, Brijesh Singh wrote:
> > Version 2 of GHCB specification introduced advertisement of a features
> > that are supported by the hypervisor. Add support to query the HV
> > features on boot.
> >
> > Version 2 of GHCB specification adds several new NAEs, most of them are
> > optional except the hypervisor feature. Now that hypervisor feature NAE
> > is implemented, so bump the GHCB maximum support protocol version.
> >
> > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > ---
> >   arch/x86/include/asm/mem_encrypt.h |  2 ++
> >   arch/x86/include/asm/sev-common.h  |  3 +++
> >   arch/x86/include/asm/sev.h         |  2 +-
> >   arch/x86/include/uapi/asm/svm.h    |  2 ++
> >   arch/x86/kernel/sev-shared.c       | 23 +++++++++++++++++++++++
> >   5 files changed, 31 insertions(+), 1 deletion(-)
>
> I think you can simplify more.
>
> The HV features are read twice - once in the decompressor stub and again
> in kernel proper - but I guess that's not such a big deal.
>
> Also, sev_hv_features can be static.
>
> Diff ontop:

The sev_hv_features is also referred during the AP creation. By caching 
the value in sev-shared.c and exporting it to others, we wanted to 
minimize VMGEXITs during the AP creation.

If we go with your patch below, then we will need to cache the 
sev_hv_features in sev.c, so that it can be later used by the AP 
creation code (see patch#22).

thanks