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 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. -- Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
