Date: Thu, 1 Feb 2024 16:55:00 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: isaku.yamahata@...el.com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v18 008/121] KVM: TDX: Initialize the TDX module when
 loading the KVM intel kernel module

On 1/23/2024 7:52 AM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> TDX requires several initialization steps for KVM to create guest TDs.
> Detect CPU feature, enable VMX (TDX is based on VMX) on all online CPUs,
> detect the TDX module availability, initialize it and disable VMX.
> 
> To enable/disable VMX on all online CPUs, utilize
> vmx_hardware_enable/disable().  The method also initializes each CPU for
> TDX.  TDX requires calling a TDX initialization function per logical
> processor (LP) before the LP uses TDX.  When the CPU is becoming online,
> call the TDX LP initialization API.  If it fails to initialize TDX, refuse
> CPU online for simplicity instead of TDX avoiding the failed LP.
> 
> There are several options on when to initialize the TDX module.  A.) kernel
> module loading time, B.) the first guest TD creation time.  A.) was chosen.
> With B.), a user may hit an error of the TDX initialization when trying to
> create the first guest TD.  The machine that fails to initialize the TDX
> module can't boot any guest TD further.  Such failure is undesirable and a
> surprise because the user expects that the machine can accommodate guest
> TD, but not.  So A.) is better than B.).
> 
> Introduce a module parameter, kvm_intel.tdx, to explicitly enable TDX KVM
> support.  It's off by default to keep the same behavior for those who don't
> use TDX.  Implement hardware_setup method to detect TDX feature of CPU and
> initialize TDX module.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
> v18:
> - Added comment in vt_hardware_enable() by Binbin.
> ---
>   arch/x86/kvm/Makefile      |  1 +
>   arch/x86/kvm/vmx/main.c    | 38 ++++++++++++++++-
>   arch/x86/kvm/vmx/tdx.c     | 84 ++++++++++++++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/x86_ops.h |  8 ++++
>   4 files changed, 129 insertions(+), 2 deletions(-)
>   create mode 100644 arch/x86/kvm/vmx/tdx.c
> 
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index 274df24b647f..5b85ef84b2e9 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -24,6 +24,7 @@ kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
>   
>   kvm-intel-$(CONFIG_X86_SGX_KVM)	+= vmx/sgx.o
>   kvm-intel-$(CONFIG_KVM_HYPERV)	+= vmx/hyperv.o vmx/hyperv_evmcs.o
> +kvm-intel-$(CONFIG_INTEL_TDX_HOST)	+= vmx/tdx.o
>   
>   kvm-amd-y		+= svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o \
>   			   svm/sev.o
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 443db8ec5cd5..1e1feaacac59 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -6,6 +6,40 @@
>   #include "nested.h"
>   #include "pmu.h"
>   
> +static bool enable_tdx __ro_after_init;
> +module_param_named(tdx, enable_tdx, bool, 0444);
> +
> +static int vt_hardware_enable(void)
> +{
> +	int ret;
> +
> +	ret = vmx_hardware_enable();
> +	if (ret || !enable_tdx)
> +		return ret;
> +
> +	ret = tdx_cpu_enable();

What's the reason for it?

vt_hardware_setup()
   -> tdx_hardware_setup()
      -> on_each_cpu(vmx_tdx_on, &vmx_tdx, true);
         -> vmx_tdx_on()
            -> tdx_cpu_enable()

ensures tdx_cpu_enable() is called once. No need to call it every 
vt_hardware_enable().

> +	if (ret)
> +		/*
> +		 * In error case, we keep the CPU offline in error case.  So
> +		 * need to revert VMXON.
> +		 */
> +		vmx_hardware_disable();
> +	return ret;
> +}
> +
> +static __init int vt_hardware_setup(void)
> +{
> +	int ret;
> +
> +	ret = vmx_hardware_setup();
> +	if (ret)
> +		return ret;
> +
> +	enable_tdx = enable_tdx && !tdx_hardware_setup(&vt_x86_ops);
> +
> +	return 0;
> +}
> +
>   #define VMX_REQUIRED_APICV_INHIBITS				\
>   	(BIT(APICV_INHIBIT_REASON_DISABLE)|			\
>   	 BIT(APICV_INHIBIT_REASON_ABSENT) |			\
> @@ -22,7 +56,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>   
>   	.hardware_unsetup = vmx_hardware_unsetup,
>   
> -	.hardware_enable = vmx_hardware_enable,
> +	.hardware_enable = vt_hardware_enable,
>   	.hardware_disable = vmx_hardware_disable,
>   	.has_emulated_msr = vmx_has_emulated_msr,
>   
> @@ -161,7 +195,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>   };
>   
>   struct kvm_x86_init_ops vt_init_ops __initdata = {
> -	.hardware_setup = vmx_hardware_setup,
> +	.hardware_setup = vt_hardware_setup,
>   	.handle_intel_pt_intr = NULL,
>   
>   	.runtime_ops = &vt_x86_ops,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> new file mode 100644
> index 000000000000..8a378fb6f1d4
> --- /dev/null
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -0,0 +1,84 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/cpu.h>
> +
> +#include <asm/tdx.h>
> +
> +#include "capabilities.h"
> +#include "x86_ops.h"
> +#include "x86.h"
> +
> +#undef pr_fmt
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +static int __init tdx_module_setup(void)
> +{
> +	int ret;
> +
> +	ret = tdx_enable();
> +	if (ret) {
> +		pr_info("Failed to initialize TDX module.\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +struct vmx_tdx_enabled {

the name is so confusing at first glance, ...

> +	cpumask_var_t vmx_enabled;
> +	atomic_t err;
> +};
> +
> +static void __init vmx_tdx_on(void *_vmx_tdx)

so is this function name.

> +{
> +	struct vmx_tdx_enabled *vmx_tdx = _vmx_tdx;
> +	int r;
> +
> +	r = vmx_hardware_enable();
> +	if (!r) {
> +		cpumask_set_cpu(smp_processor_id(), vmx_tdx->vmx_enabled);
> +		r = tdx_cpu_enable();
> +	}
> +	if (r)
> +		atomic_set(&vmx_tdx->err, r);
> +}
> +
> +static void __init vmx_off(void *_vmx_enabled)
> +{
> +	cpumask_var_t *vmx_enabled = (cpumask_var_t *)_vmx_enabled;
> +
> +	if (cpumask_test_cpu(smp_processor_id(), *vmx_enabled))
> +		vmx_hardware_disable();
> +}
> +
> +int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> +{
> +	struct vmx_tdx_enabled vmx_tdx = {
> +		.err = ATOMIC_INIT(0),
> +	};
> +	int r = 0;
> +
> +	if (!enable_ept) {
> +		pr_warn("Cannot enable TDX with EPT disabled\n");
> +		return -EINVAL;
> +	}
> +
> +	if (!zalloc_cpumask_var(&vmx_tdx.vmx_enabled, GFP_KERNEL)) {
> +		r = -ENOMEM;
> +		goto out;
> +	}
> +
> +	/* tdx_enable() in tdx_module_setup() requires cpus lock. */
> +	cpus_read_lock();
> +	on_each_cpu(vmx_tdx_on, &vmx_tdx, true);	/* TDX requires vmxon. */
> +	r = atomic_read(&vmx_tdx.err);
> +	if (!r)
> +		r = tdx_module_setup();
> +	else
> +		r = -EIO;
> +	on_each_cpu(vmx_off, &vmx_tdx.vmx_enabled, true);
> +	cpus_read_unlock();
> +	free_cpumask_var(vmx_tdx.vmx_enabled);
> +
> +out:
> +	return r;
> +}
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index bca2d27b3dfd..b44cb681f74d 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -18,6 +18,8 @@ bool kvm_is_vmx_supported(void);
>   int __init vmx_init(void);
>   void vmx_exit(void);
>   
> +__init int vmx_hardware_setup(void);

superfluous declaration.

It's added in patch 4 already.

>   extern struct kvm_x86_ops vt_x86_ops __initdata;
>   extern struct kvm_x86_init_ops vt_init_ops __initdata;
>   
> @@ -133,4 +135,10 @@ void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu);
>   #endif
>   void vmx_setup_mce(struct kvm_vcpu *vcpu);
>   
> +#ifdef CONFIG_INTEL_TDX_HOST
> +int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops);
> +#else
> +static inline int tdx_hardware_setup(struct kvm_x86_ops *x86_ops) { return -EOPNOTSUPP; }
> +#endif
> +
>   #endif /* __KVM_X86_VMX_X86_OPS_H */

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