linux-kernel - Re: [PATCH v2 2/7] KVM: x86: Extract VMXON and EFER.SVME enablement to kernel

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Message-ID: <aUvJWmZP5wLpvhnw@yilunxu-OptiPlex-7050>
Date: Wed, 24 Dec 2025 19:07:06 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: dan.j.williams@...el.com, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	Kiryl Shutsemau <kas@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	linux-coco@...ts.linux.dev, kvm@...r.kernel.org,
	Chao Gao <chao.gao@...el.com>
Subject: Re: [PATCH v2 2/7] KVM: x86: Extract VMXON and EFER.SVME enablement
 to kernel

On Wed, Dec 10, 2025 at 06:20:17AM -0800, Sean Christopherson wrote:
> On Wed, Dec 10, 2025, dan.j.williams@...el.com wrote:
> > Sean Christopherson wrote:
> > > On Sat, Dec 06, 2025, dan.j.williams@...el.com wrote:
> > > I don't think we need anything at this time.  INTEL_TDX_HOST depends on KVM_INTEL,
> > > and so without a user that needs VMXON without KVM_INTEL, I think we're good as-is.
> > > 
> > >  config INTEL_TDX_HOST
> > > 	bool "Intel Trust Domain Extensions (TDX) host support"
> > > 	depends on CPU_SUP_INTEL
> > > 	depends on X86_64
> > > 	depends on KVM_INTEL
> > 
> > ...but INTEL_TDX_HOST, it turns out, does not have any functional
> > dependencies on KVM_INTEL. At least, not since I last checked. Yes, it
> > would be silly and result in dead code today to do a build with:
> > 
> > CONFIG_INTEL_TDX_HOST=y
> > CONFIG_KVM_INTEL=n
> > 
> > However, when the TDX Connect support arrives you could have:
> > 
> > CONFIG_INTEL_TDX_HOST=y
> > CONFIG_KVM_INTEL=n
> > CONFIG_TDX_HOST_SERVICES=y
> > 
> > Where "TDX Host Services" is a driver for PCIe Link Encryption and TDX
> > Module update. Whether such configuration freedom has any practical
> > value is a separate question.
> > 
> > I am ok if the answer is, "wait until someone shows up who really wants
> > PCIe Link Encryption without KVM".
> 
> Ya, that's my answer.  At the very least, wait until TDX_HOST_SERVICES comes
> along.

I've tested the PCIe Link Encryption without KVM, with the kernel
config:

  CONFIG_INTEL_TDX_HOST=y
  CONFIG_KVM_INTEL=n
  CONFIG_TDX_HOST_SERVICES=y

and

--- /dev/null
+++ b/drivers/virt/coco/tdx-host/Kconfig
@@ -0,0 +1,10 @@
+config TDX_HOST_SERVICES
+       tristate "TDX Host Services Driver"
+       depends on INTEL_TDX_HOST
+       default m

Finally I enabled the combination successfully with a patch below, do we
need the change when TDX_HOST_SERVICES comes?

------------8<----------------------

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 80527299f859..e3e90d1fcad3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1898,7 +1898,6 @@ config INTEL_TDX_HOST
        bool "Intel Trust Domain Extensions (TDX) host support"
        depends on CPU_SUP_INTEL
        depends on X86_64
-       depends on KVM_INTEL
        depends on X86_X2APIC
        select ARCH_KEEP_MEMBLOCK
        depends on CONTIG_ALLOC
diff --git a/arch/x86/include/asm/virt.h b/arch/x86/include/asm/virt.h
index 77a366afd9f7..26bbf0f21575 100644
--- a/arch/x86/include/asm/virt.h
+++ b/arch/x86/include/asm/virt.h
@@ -6,7 +6,7 @@

 typedef void (cpu_emergency_virt_cb)(void);

-#if IS_ENABLED(CONFIG_KVM_X86)
+#if IS_ENABLED(CONFIG_KVM_X86) || IS_ENABLED(CONFIG_INTEL_TDX_HOST)
 extern bool virt_rebooting;

 void __init x86_virt_init(void);
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 278f08194ec8..28fe309093ed 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -134,7 +134,7 @@ config X86_SGX_KVM
 config KVM_INTEL_TDX
        bool "Intel Trust Domain Extensions (TDX) support"
        default y
-       depends on INTEL_TDX_HOST
+       depends on INTEL_TDX_HOST && KVM_INTEL
        select KVM_GENERIC_MEMORY_ATTRIBUTES
        select HAVE_KVM_ARCH_GMEM_POPULATE
        help
diff --git a/arch/x86/virt/Makefile b/arch/x86/virt/Makefile
index 6e485751650c..85ed7a06ed88 100644
--- a/arch/x86/virt/Makefile
+++ b/arch/x86/virt/Makefile
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y  += svm/ vmx/

-obj-$(subst m,y,$(CONFIG_KVM_X86)) += hw.o
\ No newline at end of file
+obj-$(CONFIG_INTEL_TDX_HOST) += hw.o
+obj-$(subst m,y,$(CONFIG_KVM_X86)) += hw.o
diff --git a/arch/x86/virt/hw.c b/arch/x86/virt/hw.c
index 986e780cf438..31ea89069a93 100644
--- a/arch/x86/virt/hw.c
+++ b/arch/x86/virt/hw.c
@@ -48,7 +48,7 @@ static void x86_virt_invoke_kvm_emergency_callback(void)
                kvm_callback();
 }

-#if IS_ENABLED(CONFIG_KVM_INTEL)
+#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_INTEL_TDX_HOST)
 static DEFINE_PER_CPU(struct vmcs *, root_vmcs);

 static int x86_virt_cpu_vmxon(void)
@@ -257,7 +257,8 @@ static __init int x86_svm_init(void) { return -EOPNOTSUPP; }
 ({                                                     \
        int __r;                                        \
                                                        \
-       if (IS_ENABLED(CONFIG_KVM_INTEL) &&             \
+       if ((IS_ENABLED(CONFIG_KVM_INTEL) ||            \
+            IS_ENABLED(CONFIG_INTEL_TDX_HOST)) &&      \
            cpu_feature_enabled(X86_FEATURE_VMX))       \
                __r = x86_vmx_##fn();                   \
        else if (IS_ENABLED(CONFIG_KVM_AMD) &&          \

>