On Tue, May 24, 2022 at 08:56:43PM +0000, Vishal Annapurve wrote:
This series implements selftests targeting the feature floated by Chao via: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kerne...
Below changes aim to test the fd based approach for guest private memory in context of SEV/SEV-ES VMs executing on AMD SEV/SEV-ES compatible platforms.
Hi Vishal,
Thanks for posting this!
Nikunj and I have been working on a test tree with UPM support for SEV and SEV-SNP. I hit some issues getting your selftests to work against our tree since some of the HC_MAP_GPA_RANGE handling for SEV was stepping on the kernel handling you'd added for the UPM selftests.
I ended up adding a KVM_CAP_UNMAPPED_PRIVATE_MEM to distinguish between the 2 modes. With UPM-mode enabled it basically means KVM can/should enforce that all private guest pages are backed by private memslots, and enable a couple platform-specific hooks to handle MAP_GPA_RANGE, and queries from MMU on whether or not an NPT fault is for a private page or not. SEV uses these hooks to manage its encryption bitmap, and uses that bitmap as the authority on whether or not a page is encrypted. SNP uses GHCB page-state-change requests so MAP_GPA_RANGE is a no-op there, but uses the MMU hook to indicate whether a fault is private based on the page fault flags.
When UPM-mode isn't enabled, MAP_GPA_RANGE just gets passed on to userspace as before, and platform-specific hooks above are no-ops. That's the mode your SEV self-tests ran in initially. I added a test that runs the PrivateMemoryPrivateAccess in UPM-mode, where the guest's OS memory is also backed by private memslot and the platform hooks are enabled, and things seem to still work okay there. I only added a UPM-mode test for the PrivateMemoryPrivateAccess one though so far. I suppose we'd want to make sure it works exactly as it did with UPM-mode disabled, but I don't see why it wouldn't.
But probably worth having some discussion on how exactly we should define this mode, and whether that meshes with what TDX folks are planning.
I've pushed my UPM-mode selftest additions here: https://github.com/mdroth/linux/commits/sev_upm_selftests_rfc_v1_upmmode
And the UPM SEV/SEV-SNP tree I'm running them against (DISCLAIMER: EXPERIMENTAL): https://github.com/mdroth/linux/commits/pfdv6-on-snpv6-upm1
Thanks!
-Mike