On Fri, Dec 23, 2022 at 05:56:50PM +0100, Borislav Petkov wrote: > On Wed, Dec 14, 2022 at 01:39:55PM -0600, Michael Roth wrote: > > + bool (*private_mem_enabled)(struct kvm *kvm); > > This looks like a function returning boolean to me. IOW, you can > simplify this to: The semantics and existing uses of KVM_X86_OP_OPTIONAL_RET0() gave me the impression it needed to return an integer value, since by default if a platform doesn't implement the op it would "return 0", and so could still be called unconditionally. Maybe that's not actually enforced, by it seems awkward to try to use a bool return instead. At least for KVM_X86_OP_OPTIONAL_RET0(). However, we could just use KVM_X86_OP() to declare it so we can cleanly use a function that returns bool, and then we just need to do: bool kvm_arch_has_private_mem(struct kvm *kvm) { if (kvm_x86_ops.private_mem_enabled) return static_call(kvm_x86_private_mem_enabled)(kvm); } instead of relying on default return value. So I'll take that approach and adopt your other suggested changes. ... On a separate topic though, at a high level, this hook is basically a way for platform-specific code to tell generic KVM code that private memslots are supported by overriding the kvm_arch_has_private_mem() weak reference. In this case the AMD platform is using using kvm->arch.upm_mode flag to convey that, which is in turn set by the KVM_CAP_UNMAPPED_PRIVATE_MEMORY introduced in this series. But if, as I suggested in response to your PATCH 2 comments, we drop KVM_CAP_UNAMMPED_PRIVATE_MEMORY in favor of KVM_SET_SUPPORTED_MEMORY_ATTRIBUTES ioctl to enable "UPM mode" in SEV/SNP code, then we need to rethink things a bit, since KVM_SET_MEMORY_ATTRIBUTES in-part relies on kvm_arch_has_private_mem() to determine what flags are supported, whereas SEV/SNP code would be using what was set by KVM_SET_MEMORY_ATTRIBUTES to determine the return value in kvm_arch_has_private_mem(). So, for AMD, the return value of kvm_arch_has_private_mem() needs to rely on something else. Maybe the logic can just be: bool svm_private_mem_enabled(struct kvm *kvm) { return sev_enabled(kvm) || sev_snp_enabled(kvm) } (at least in the context of this patchset where UPM support is added for both SEV and SNP). So I'll plan to make that change as well. -Mike > > diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h > index 82ba4a564e58..4449aeff0dff 100644 > --- a/arch/x86/include/asm/kvm-x86-ops.h > +++ b/arch/x86/include/asm/kvm-x86-ops.h > @@ -129,6 +129,7 @@ KVM_X86_OP(msr_filter_changed) > KVM_X86_OP(complete_emulated_msr) > KVM_X86_OP(vcpu_deliver_sipi_vector) > KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons); > +KVM_X86_OP_OPTIONAL_RET0(private_mem_enabled); > > #undef KVM_X86_OP > #undef KVM_X86_OP_OPTIONAL > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 1da0474edb2d..1b4b89ddeb55 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1574,6 +1574,7 @@ struct kvm_x86_ops { > > void (*load_mmu_pgd)(struct kvm_vcpu *vcpu, hpa_t root_hpa, > int root_level); > + bool (*private_mem_enabled)(struct kvm *kvm); > > bool (*has_wbinvd_exit)(void); > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index ce362e88a567..73b780fa4653 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -4680,6 +4680,14 @@ static int svm_vm_init(struct kvm *kvm) > return 0; > } > > +static bool svm_private_mem_enabled(struct kvm *kvm) > +{ > + if (sev_guest(kvm)) > + return kvm->arch.upm_mode; > + > + return IS_ENABLED(CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING); > +} > + > static struct kvm_x86_ops svm_x86_ops __initdata = { > .name = "kvm_amd", > > @@ -4760,6 +4768,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = { > > .vcpu_after_set_cpuid = svm_vcpu_after_set_cpuid, > > + .private_mem_enabled = svm_private_mem_enabled, > + > .has_wbinvd_exit = svm_has_wbinvd_exit, > > .get_l2_tsc_offset = svm_get_l2_tsc_offset, > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 823646d601db..9a1ca59d36a4 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -12556,6 +12556,11 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, > } > EXPORT_SYMBOL_GPL(__x86_set_memory_region); > > +bool kvm_arch_has_private_mem(struct kvm *kvm) > +{ > + return static_call(kvm_x86_private_mem_enabled)(kvm); > +} > + > void kvm_arch_pre_destroy_vm(struct kvm *kvm) > { > kvm_mmu_pre_destroy_vm(kvm); > > -- > Regards/Gruss, > Boris. > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpeople.kernel.org%2Ftglx%2Fnotes-about-netiquette&data=05%7C01%7Cmichael.roth%40amd.com%7C319e89ce555a46eace4d08dae506b51a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638074114318137471%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=aG11K7va1BhemwlKCKKdcIXEwXGUzImYL%2BZ9%2FQ7XToI%3D&reserved=0