On Fri, 2024-05-24 at 00:55 -0700, Isaku Yamahata wrote: > On Thu, May 23, 2024 at 06:27:49PM +0000, > "Edgecombe, Rick P" <rick.p.edgecombe@xxxxxxxxx> wrote: > > > On Wed, 2024-05-22 at 17:01 -0700, Isaku Yamahata wrote: > > > Ok, Let's include the patch. > > > > We were discussing offline, that actually the existing behavior of > > kvm_mmu_max_gfn() can be improved for normal VMs. It would be more proper to > > trigger it off of the GFN range supported by EPT level, than the host > > MAXPA. > > > > Today I was thinking, to fix this would need somthing like an > > x86_ops.max_gfn(), > > so it could get at VMX stuff (usage of 4/5 level EPT). If that exists we > > might > > as well just call it directly in kvm_mmu_max_gfn(). > > > > Then for TDX we could just provide a TDX implementation, rather than stash > > the > > GFN on the kvm struct? Instead it could use gpaw stashed on struct kvm_tdx. > > The > > op would still need to be take a struct kvm. > > > > What do you think of that alternative? > > I don't see benefit of x86_ops.max_gfn() compared to kvm->arch.max_gfn. > But I don't have strong preference. Either way will work. The non-TDX VM's won't need per-VM data, right? So it's just unneeded extra state per-vm. > > The max_gfn for the guest is rather static once the guest is created and > initialized. Also the existing codes that use max_gfn expect that the value > doesn't change. So we can use x86_ops.vm_init() to determine the value for > VMX > and TDX. If we introduced x86_ops.max_gfn(), the implementation will be > simply > return kvm_vmx->max_gfn or return kvm_tdx->max_gfn. (We would have similar for > SVM and SEV.) So I don't see benefit of x86_ops.max_gfn() than > kvm->arch.max_gfn. For TDX it will be based on the shared bit, so we actually already have the per- vm data we need. So we don't even need both gfn_shared_mask and max_gfn for TDX.
