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Thu, 25 Jun 2026 10:04:12 -0700 (PDT) Date: Thu, 25 Jun 2026 10:04:11 -0700 In-Reply-To: <20260604023314.3907511-2-binbin.wu@linux.intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260604023314.3907511-1-binbin.wu@linux.intel.com> <20260604023314.3907511-2-binbin.wu@linux.intel.com> Message-ID: Subject: Re: [RFC PATCH v2 1/4] KVM: x86: TDX: Track supported configurable CPUID bits From: Sean Christopherson To: Binbin Wu Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, rick.p.edgecombe@intel.com, xiaoyao.li@intel.com, chao.gao@intel.com, kai.huang@intel.com Content-Type: text/plain; charset="us-ascii" On Thu, Jun 04, 2026, Binbin Wu wrote: > --- > arch/x86/kvm/vmx/tdx.c | 174 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 174 insertions(+) > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > index ffe9d0db58c5..e0567088ebf5 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -52,6 +52,178 @@ > __TDX_BUG_ON(__err, #__fn, __kvm, ", " #a1 " 0x%llx, " #a2 ", 0x%llx, " #a3 " 0x%llx", \ > a1, a2, a3) > > +#define TDX_CPUID_IGNORE_INDEX BIT(0) > +struct tdx_supported_cpuid_reg { > + u32 function; > + u32 index; > + u8 flags; > + u8 reg; > + u32 mask; > +}; > + > +/* > + * Multi-bit fields are statically initialized, feature bits are initialized > + * in tdx_initialize_cpu_cfg_caps(). > + */ > +static struct tdx_supported_cpuid_reg tdx_kvm_supported_cpuid[] __ro_after_init = { > + { 0x1, 0, 0, CPUID_EAX, GENMASK_U32(27, 16) | GENMASK_U32(13, 0) }, > + { 0x1, 0, 0, CPUID_EBX, GENMASK_U32(23, 16) }, > + { 0x1, 0, 0, CPUID_ECX, 0 }, > + { 0x1, 0, 0, CPUID_EDX, 0 }, > + { 0x4, 0, TDX_CPUID_IGNORE_INDEX, CPUID_EAX, ~GENMASK_U32(13, 10) }, > + { 0x4, 0, TDX_CPUID_IGNORE_INDEX, CPUID_EBX, GENMASK_U32(31, 12) }, > + { 0x4, 0, TDX_CPUID_IGNORE_INDEX, CPUID_ECX, GENMASK_U32(31, 0) }, > + { 0x4, 0, TDX_CPUID_IGNORE_INDEX, CPUID_EDX, GENMASK_U32(2, 0) }, > + { 0x7, 0, 0, CPUID_EBX, 0 }, > + { 0x7, 0, 0, CPUID_ECX, 0 }, > + { 0x7, 0, 0, CPUID_EDX, 0 }, > + { 0x7, 1, 0, CPUID_EAX, 0 }, > + { 0x7, 1, 0, CPUID_EDX, 0 }, > + { 0x7, 2, 0, CPUID_EDX, 0 }, > + { 0x18, 0, TDX_CPUID_IGNORE_INDEX, CPUID_EDX, GENMASK_U32(25, 14) }, > + { 0x1E, 1, 0, CPUID_EAX, 0 }, > + { 0x1F, 0, TDX_CPUID_IGNORE_INDEX, CPUID_EAX, GENMASK_U32(4, 0) }, > + { 0x1F, 0, TDX_CPUID_IGNORE_INDEX, CPUID_EBX, GENMASK_U32(15, 0) }, > + { 0x1F, 0, TDX_CPUID_IGNORE_INDEX, CPUID_ECX, GENMASK_U32(15, 0) }, > + /* See comments in td_init_cpuid_entry2() for CPUID 0x80000008 EAX[23:16]. */ > + { 0x80000008, 0, 0, CPUID_EAX, GENMASK_U32(23, 16) | GENMASK_U32(7, 0) }, > + { 0x80000008, 0, 0, CPUID_EBX, 0 }, For non-feature bits, I think I would rather handle them entirely at runtime via switch statement(s). Realistically, CPUID.0x1.E{A,B}X are never going to be repurposed to hold feature bits, and so generating a mask of allowed bits adds unnecessary cognitive load and maintenance. Ditto for CPUID 0x4, 0x18, and 0x1F. CPUID.0x1E is a bit different because it's kinda sorta a feature? That one is probably worth restricting, but again that's easy to do in a case-statement. Then for the feature bits, there should be no need to define a separate structure, just do "u32 kvm_tdx_cpu_caps[NR_KVM_CPU_CAPS]". Then KVM can even further restrict that array with kvm_cpu_caps (though it might take some creativity to deal with things like MWAIT). Because generally speaking, KVM shouldn't allow features that KVM doesn't support for non-TDX VMs.