9 Jul
2020
9 Jul
'20
12:11 p.m.
On 09/07/20 11:55, Mohammed Gamal wrote:
Ideally we would simply outlaw (3), but it's hard for backward compatibility reasons. Second best solution is a flag somewhere (msr, cpuid, ...) telling the guest firmware "you can use GUEST_MAXPHYADDR, we guarantee it is <= HOST_MAXPHYADDR". Problem is GUEST_MAXPHYADDR > HOST_MAXPHYADDR is actually a supported configuration on some setups. Namely when memory encryption is enabled on AMD CPUs[1].
It's not that bad since there's two MAXPHYADDRs, the one in CPUID and the one computed internally by the kernel. GUEST_MAXPHYADDR greater than the host CPUID maxphyaddr is never supported. Paolo