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Peter Anvin" , kvm@vger.kernel.org, linux-doc@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Wed, Apr 23, 2025, Zack Rusin wrote: > On Wed, Apr 23, 2025 at 3:56=E2=80=AFAM Xin Li wrote: > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > index 300cef9a37e2..5dc57bc57851 100644 > > > --- a/arch/x86/kvm/x86.c > > > +++ b/arch/x86/kvm/x86.c > > > @@ -4653,6 +4653,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kv= m, long ext) > > > #ifdef CONFIG_KVM_VMWARE > > > case KVM_CAP_X86_VMWARE_BACKDOOR: > > > case KVM_CAP_X86_VMWARE_HYPERCALL: > > > + case KVM_CAP_X86_VMWARE_NESTED_BACKDOOR_L0: I would probably omit the L0, because KVM could be running as L1. > > > #endif > > > r =3D 1; > > > break; > > > @@ -6754,6 +6755,13 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, > > > kvm->arch.vmware.hypercall_enabled =3D cap->args[0]; > > > r =3D 0; > > > break; > > > + case KVM_CAP_X86_VMWARE_NESTED_BACKDOOR_L0: > > > + r =3D -EINVAL; > > > + if (cap->args[0] & ~1) > > > > Replace ~1 with a macro for better readability please. >=20 > Are you sure about that? This code is already used elsewhere in the > file (for KVM_CAP_EXIT_ON_EMULATION_FAILURE) so, ignoring the fact > that it's arguable whether IS_ZERO_OR_ONE is more readable than & ~1, > if we use a macro for the vmware caps and not for > KVM_CAP_EXIT_ON_EMULATION_FAILURE then the code would be inconsistent > and that decreases the readability. Heh, KVM_CAP_EXIT_ON_EMULATION_FAILURE is the odd one out. Even if that we= ren't the case, this is one of the situations where diverging from the existing c= ode is desirable, because the existing code is garbage. arch/x86/kvm/x86.c: if (cap->args[0] & ~kvm_caps.supported_quir= ks) arch/x86/kvm/x86.c: if (cap->args[0] & ~KVM_X2APIC_API_VALID_FL= AGS) arch/x86/kvm/x86.c: if (cap->args[0] & ~kvm_get_allowed_disable= _exits()) arch/x86/kvm/x86.c: (cap->args[0] & ~KVM_X86_DISABLE_EXITS_= PAUSE)) arch/x86/kvm/x86.c: if (cap->args[0] & ~KVM_MSR_EXIT_REASON_VAL= ID_MASK) arch/x86/kvm/x86.c: if (cap->args[0] & ~KVM_BUS_LOCK_DETECTION_= VALID_MODE) arch/x86/kvm/x86.c: if (cap->args[0] & ~KVM_EXIT_HYPERCALL_VALI= D_MASK) { arch/x86/kvm/x86.c: if (cap->args[0] & ~1) arch/x86/kvm/x86.c: if (!enable_pmu || (cap->args[0] & ~KVM_CAP= _PMU_VALID_MASK)) arch/x86/kvm/x86.c: if ((u32)cap->args[0] & ~KVM_X86_NOTIFY_VME= XIT_VALID_BITS) virt/kvm/kvm_main.c: if (cap->flags || (cap->args[0] & ~allowed_= options)) > Or are you saying that since I'm already there you'd like to see a > completely separate patch that defines some kind of IS_ZERO_OR_ONE > macro for KVM, use it for KVM_CAP_EXIT_ON_EMULATION_FAILURE and, once > that lands then I can make use of it in this series? Xin is suggesting that you add a macro in arch/x86/include/uapi/asm/kvm.h t= o #define which bits are valid and which bits are reserved. At a glance, you can kill multiple birds with one stone. Rather than add t= hree separate capabilities, add one capability and then a variety of flags. E.g= . #define KVM_X86_VMWARE_HYPERCALL _BITUL(0) #define KVM_X86_VMWARE_BACKDOOR _BITUL(1) #define KVM_X86_VMWARE_NESTED_BACKDOOR _BITUL(2) #define KVM_X86_VMWARE_VALID_FLAGS (KVM_X86_VMWARE_HYPERCALL | KVM_X86_VMWARE_BACKDOOR | KVM_X86_VMWARE_NESTED_BACKDOOR) case KVM_CAP_X86_VMWARE_EMULATION: r =3D -EINVAL; if (cap->args[0] & ~KVM_X86_VMWARE_VALID_FLAGS) break; mutex_lock(&kvm->lock); if (!kvm->created_vcpus) { if (cap->args[0] & KVM_X86_VMWARE_HYPERCALL) kvm->arch.vmware.hypercall_enabled =3D true; if (cap->args[0] & KVM_X86_VMWARE_BACKDOOR) kvm->arch.vmware.backdoor_enabled; if (cap->args[0] & KVM_X86_VMWARE_NESTED_BACKDOOR) kvm->arch.vmware.nested_backdoor_enabled =3D true; r =3D 0; } mutex_unlock(&kvm->lock); break; That approach wouldn't let userspace disable previously enabled VMware capa= bilities, but unless there's a use case for doing so, that should be a non-issue.