On Fri, Apr 8, 2022, at 2:05 PM, Vishal Annapurve wrote:
This series implements selftests targeting the feature floated by Chao via: https://lore.kernel.org/linux-mm/20220310140911.50924-1-chao.p.peng@linux.in...
Below changes aim to test the fd based approach for guest private memory in context of normal (non-confidential) VMs executing on non-confidential platforms.
Confidential platforms along with the confidentiality aware software stack support a notion of private/shared accesses from the confidential VMs. Generally, a bit in the GPA conveys the shared/private-ness of the access. Non-confidential platforms don't have a notion of private or shared accesses from the guest VMs. To support this notion, KVM_HC_MAP_GPA_RANGE is modified to allow marking an access from a VM within a GPA range as always shared or private. Any suggestions regarding implementing this ioctl alternatively/cleanly are appreciated.
This is fantastic. I do think we need to decide how this should work in general. We have a few platforms with somewhat different properties:
TDX: The guest decides, per memory access (using a GPA bit), whether an access is private or shared. In principle, the same address could be *both* and be distinguished by only that bit, and the two addresses would refer to different pages.
SEV: The guest decides, per memory access (using a GPA bit), whether an access is private or shared. At any given time, a physical address (with that bit masked off) can be private, shared, or invalid, but it can't be valid as private and shared at the same time.
pKVM (currently, as I understand it): the guest decides by hypercall, in advance of an access, which addresses are private and which are shared.
This series, if I understood it correctly, is like TDX except with no hardware security.
Sean or Chao, do you have a clear sense of whether the current fd-based private memory proposal can cleanly support SEV and pKVM? What, if anything, needs to be done on the API side to get that working well? I don't think we need to support SEV or pKVM right away to get this merged, but I do think we should understand how the API can map to them.