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Peter Anvin" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, Changyuan Lyu , Sashiko Content-Type: text/plain; charset="us-ascii" On Fri, Oct 23, 2026, Binbin Wu wrote: > On 10/23/2026 5:01 AM, Sean Christopherson wrote: > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > > index 271c2f94b8dd..37d088f6f7a8 100644 > > --- a/arch/x86/kvm/vmx/tdx.c > > +++ b/arch/x86/kvm/vmx/tdx.c > > @@ -2,6 +2,7 @@ > > #include > > #include > > #include > > +#include > > #include > > #include > > #include > > @@ -163,12 +164,23 @@ static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char i > > > > entry->function = (u32)td_conf->cpuid_config_leaves[idx]; > > entry->index = td_conf->cpuid_config_leaves[idx] >> 32; > > + entry->flags = 0; > > entry->eax = (u32)td_conf->cpuid_config_values[idx][0]; > > entry->ebx = td_conf->cpuid_config_values[idx][0] >> 32; > > entry->ecx = (u32)td_conf->cpuid_config_values[idx][1]; > > entry->edx = td_conf->cpuid_config_values[idx][1] >> 32; > > > > - if (entry->index == KVM_TDX_CPUID_NO_SUBLEAF) > > + WARN_ON_ONCE(cpuid_function_is_indexed(entry->function) != > > + (entry->index != KVM_TDX_CPUID_NO_SUBLEAF)); > > + > > + /* > > + * Explicitly zero the index when it's not significant, even though it > > + * _should_ be meaningless. Userspace relies on the index being zero > > + * (the ABI was inherited from KVM_GET_SUPPORTED_CPUID). > > + */ > > + if (cpuid_function_is_indexed(entry->function)) > > If the information about whether the entry is indexed mismatched, i.e. the > warning above fired, should we use the information from the TDX module as the > standard? IMO, no. All of this information is available at module load. If we want to harden KVM (and we probably should), then we should apply these sanity checks (or equivalents) during tdx_hardware_setup() and disable TDX if any of them fail. Anything else is a hope and a prayer.