Subject: Re: [PATCH v2 31/50] KVM: x86: Do CPU compatibility checks in x86 code

From: Isaku Yamahata <[email-masked]>
Date: Mon, 5 Dec 2022 12:52:46 -0800

On Wed, Nov 30, 2022 at 11:09:15PM +0000,
Sean Christopherson <[email-masked]> wrote:

> Move the CPU compatibility checks to pure x86 code, i.e. drop x86's use
> of the common kvm_x86_check_cpu_compat() arch hook.  x86 is the only
> architecture that "needs" to do per-CPU compatibility checks, moving
> the logic to x86 will allow dropping the common code, and will also
> give x86 more control over when/how the compatibility checks are
> performed, e.g. TDX will need to enable hardware (do VMXON) in order to
> perform compatibility checks.
> 
> Signed-off-by: Sean Christopherson <[email-masked]>
> ---
>  arch/x86/kvm/svm/svm.c |  2 +-
>  arch/x86/kvm/vmx/vmx.c |  2 +-
>  arch/x86/kvm/x86.c     | 49 ++++++++++++++++++++++++++++++++----------
>  3 files changed, 40 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 19e81a99c58f..d7ea1c1175c2 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -5103,7 +5103,7 @@ static int __init svm_init(void)
>  	 * Common KVM initialization _must_ come last, after this, /dev/kvm is
>  	 * exposed to userspace!
>  	 */
> -	r = kvm_init(&svm_init_ops, sizeof(struct vcpu_svm),
> +	r = kvm_init(NULL, sizeof(struct vcpu_svm),
>  		     __alignof__(struct vcpu_svm), THIS_MODULE);
>  	if (r)
>  		goto err_kvm_init;
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 654d81f781da..8deb1bd60c10 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -8592,7 +8592,7 @@ static int __init vmx_init(void)
>  	 * Common KVM initialization _must_ come last, after this, /dev/kvm is
>  	 * exposed to userspace!
>  	 */
> -	r = kvm_init(&vmx_init_ops, sizeof(struct vcpu_vmx),
> +	r = kvm_init(NULL, sizeof(struct vcpu_vmx),
>  		     __alignof__(struct vcpu_vmx), THIS_MODULE);
>  	if (r)
>  		goto err_kvm_init;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 66f16458aa97..3571bc968cf8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9277,10 +9277,36 @@ static inline void kvm_ops_update(struct kvm_x86_init_ops *ops)
>  	kvm_pmu_ops_update(ops->pmu_ops);
>  }
>  
> +struct kvm_cpu_compat_check {
> +	struct kvm_x86_init_ops *ops;
> +	int *ret;

minor nitpick: just int ret. I don't see the necessity of the pointer.
Anyway overall it looks good to me.

Reviewed-by: Isaku Yamahata <[email-masked]>

> +};
> +
> +static int kvm_x86_check_processor_compatibility(struct kvm_x86_init_ops *ops)
> +{
> +	struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
> +
> +	WARN_ON(!irqs_disabled());
> +
> +	if (__cr4_reserved_bits(cpu_has, c) !=
> +	    __cr4_reserved_bits(cpu_has, &boot_cpu_data))
> +		return -EIO;
> +
> +	return ops->check_processor_compatibility();
> +}
> +
> +static void kvm_x86_check_cpu_compat(void *data)
> +{
> +	struct kvm_cpu_compat_check *c = data;
> +
> +	*c->ret = kvm_x86_check_processor_compatibility(c->ops);
> +}
> +
>  static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>  {
> +	struct kvm_cpu_compat_check c;
>  	u64 host_pat;
> -	int r;
> +	int r, cpu;
>  
>  	if (kvm_x86_ops.hardware_enable) {
>  		pr_err("kvm: already loaded vendor module '%s'\n", kvm_x86_ops.name);
> @@ -9360,6 +9386,14 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>  	if (r != 0)
>  		goto out_mmu_exit;
>  
> +	c.ret = &r;
> +	c.ops = ops;
> +	for_each_online_cpu(cpu) {
> +		smp_call_function_single(cpu, kvm_x86_check_cpu_compat, &c, 1);
> +		if (r < 0)

Here it can be "c.ret < 0".

> +			goto out_hardware_unsetup;
> +	}
> +
>  	/*
>  	 * Point of no return!  DO NOT add error paths below this point unless
>  	 * absolutely necessary, as most operations from this point forward
> @@ -9402,6 +9436,8 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>  	kvm_init_msr_list();
>  	return 0;
>  
> +out_hardware_unsetup:
> +	ops->runtime_ops->hardware_unsetup();
>  out_mmu_exit:
>  	kvm_mmu_vendor_module_exit();
>  out_free_percpu:
> @@ -12037,16 +12073,7 @@ void kvm_arch_hardware_disable(void)
>  
>  int kvm_arch_check_processor_compat(void *opaque)
>  {
> -	struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
> -	struct kvm_x86_init_ops *ops = opaque;
> -
> -	WARN_ON(!irqs_disabled());
> -
> -	if (__cr4_reserved_bits(cpu_has, c) !=
> -	    __cr4_reserved_bits(cpu_has, &boot_cpu_data))
> -		return -EIO;
> -
> -	return ops->check_processor_compatibility();
> +	return 0;
>  }
>  
>  bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu)
> -- 
> 2.38.1.584.g0f3c55d4c2-goog
> 

-- 
Isaku Yamahata <[email-masked]>