Re: [PATCH 7/7] KVM: TDX: Add TSX_CTRL msr into uret_msrs list

[Sean Christopherson <seanjc@google.com>]

On Fri, Nov 22, 2024, Chao Gao wrote:
> >+static bool tdparams_tsx_supported(struct kvm_cpuid2 *cpuid)
> >+{
> >+	const struct kvm_cpuid_entry2 *entry;
> >+	u64 mask;
> >+	u32 ebx;
> >+
> >+	entry = kvm_find_cpuid_entry2(cpuid->entries, cpuid->nent, 0x7, 0);
> >+	if (entry)
> >+		ebx = entry->ebx;
> >+	else
> >+		ebx = 0;
> >+
> >+	mask = __feature_bit(X86_FEATURE_HLE) | __feature_bit(X86_FEATURE_RTM);
> >+	return ebx & mask;
> >+}
> >+
> > static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
> > 			struct kvm_tdx_init_vm *init_vm)
> > {
> >@@ -1299,6 +1322,7 @@ static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
> > 	MEMCPY_SAME_SIZE(td_params->mrowner, init_vm->mrowner);
> > 	MEMCPY_SAME_SIZE(td_params->mrownerconfig, init_vm->mrownerconfig);
> > 
> >+	to_kvm_tdx(kvm)->tsx_supported = tdparams_tsx_supported(cpuid);
> > 	return 0;
> > }
> > 
> >@@ -2272,6 +2296,11 @@ static int __init __tdx_bringup(void)
> > 			return -EIO;
> > 		}
> > 	}
> >+	tdx_uret_tsx_ctrl_slot = kvm_find_user_return_msr(MSR_IA32_TSX_CTRL);
> >+	if (tdx_uret_tsx_ctrl_slot == -1 && boot_cpu_has(X86_FEATURE_MSR_TSX_CTRL)) {
> >+		pr_err("MSR_IA32_TSX_CTRL isn't included by kvm_find_user_return_msr\n");
> >+		return -EIO;
> >+	}
> > 
> > 	/*
> > 	 * Enabling TDX requires enabling hardware virtualization first,
> >diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> >index 48cf0a1abfcc..815ff6bdbc7e 100644
> >--- a/arch/x86/kvm/vmx/tdx.h
> >+++ b/arch/x86/kvm/vmx/tdx.h
> >@@ -29,6 +29,14 @@ struct kvm_tdx {
> > 	u8 nr_tdcs_pages;
> > 	u8 nr_vcpu_tdcx_pages;
> > 
> >+	/*
> >+	 * Used on each TD-exit, see tdx_user_return_msr_update_cache().
> >+	 * TSX_CTRL value on TD exit
> >+	 * - set 0     if guest TSX enabled
> >+	 * - preserved if guest TSX disabled
> >+	 */
> >+	bool tsx_supported;
> 
> Is it possible to drop this boolean and tdparams_tsx_supported()? I think we
> can use the guest_can_use() framework instead.

Yeah, though that optimized handling will soon come for free[*], and I plan on
landing that sooner than TDX, so don't fret too much over this.

[*] https://lore.kernel.org/all/20240517173926.965351-1-seanjc@google.com