linux-kernel - Re: [PATCH v3 14/18] KVM: SVM: Check that the current CPU supports SVM in kvm_is_svm

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Message-ID: <393d84bef4c5896b896ffe94559ebe2d8173a8c5.camel@intel.com>
Date:   Mon, 22 May 2023 23:18:45 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Gao, Chao" <chao.gao@...el.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v3 14/18] KVM: SVM: Check that the current CPU supports
 SVM in kvm_is_svm_supported()

On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> Check "this" CPU instead of the boot CPU when querying SVM support so that
> the per-CPU checks done during hardware enabling actually function as
> intended, i.e. will detect issues where SVM isn't support on all CPUs.
> 
> Disable migration for the use from svm_init() mostly so that the standard
> accessors for the per-CPU data can be used without getting yelled at by
> CONFIG_DEBUG_PREEMPT=y sanity checks.  Preventing the "disabled by BIOS"
> error message from reporting the wrong CPU is largely a bonus, as ensuring
> a stable CPU during module load is a non-goal for KVM.

"non-goal for KVM (at least for now)" ? :)

> 
> Link: https://lore.kernel.org/all/ZAdxNgv0M6P63odE@google.com
> Cc: Kai Huang <kai.huang@...el.com>
> Cc: Chao Gao <chao.gao@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Kai Huang <kai.huang@...el.com>

> ---
>  arch/x86/kvm/svm/svm.c | 25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index b347173b4e29..cf5f3880751b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -523,18 +523,20 @@ static void svm_init_osvw(struct kvm_vcpu *vcpu)
>  		vcpu->arch.osvw.status |= 1;
>  }
>  
> -static bool kvm_is_svm_supported(void)
> +static bool __kvm_is_svm_supported(void)
>  {
> -	int cpu = raw_smp_processor_id();
> +	int cpu = smp_processor_id();
> +	struct cpuinfo_x86 *c = &cpu_data(cpu);
> +
>  	u64 vm_cr;
>  
> -	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
> -	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON) {
> +	if (c->x86_vendor != X86_VENDOR_AMD &&
> +	    c->x86_vendor != X86_VENDOR_HYGON) {
>  		pr_err("CPU %d isn't AMD or Hygon\n", cpu);
>  		return false;
>  	}
>  
> -	if (!boot_cpu_has(X86_FEATURE_SVM)) {
> +	if (!cpu_has(c, X86_FEATURE_SVM)) {
>  		pr_err("SVM not supported by CPU %d\n", cpu);
>  		return false;
>  	}
> @@ -553,9 +555,20 @@ static bool kvm_is_svm_supported(void)
>  	return true;
>  }
>  
> +static bool kvm_is_svm_supported(void)
> +{
> +	bool supported;
> +
> +	migrate_disable();
> +	supported = __kvm_is_svm_supported();
> +	migrate_enable();
> +
> +	return supported;
> +}
> +
>  static int svm_check_processor_compat(void)
>  {
> -	if (!kvm_is_svm_supported())
> +	if (!__kvm_is_svm_supported())
>  		return -EIO;
>  
>  	return 0;
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>