On 8/23/21 1:25 PM, Brijesh Singh wrote:

On 8/23/21 4:47 AM, Borislav Petkov wrote:

quoted

On Fri, Aug 20, 2021 at 10:19:02AM -0500, Brijesh Singh wrote:

quoted

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 <redacted>
---
  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).

Let me take it back, I didn't realize that sev.c includes the 
sev-shared.c. So your patch will work fine. sorry about the noise.