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Subject: Re: [PATCH 2/4] kvm: svm: Enable UMIP feature on AMD
To:     "Moger, Babu" <Babu.Moger@amd.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
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        "sean.j.christopherson@intel.com" <sean.j.christopherson@intel.com>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
        "wanpengli@tencent.com" <wanpengli@tencent.com>,
        "jmattson@google.com" <jmattson@google.com>
Cc:     "x86@kernel.org" <x86@kernel.org>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "luto@kernel.org" <luto@kernel.org>,
        "zohar@linux.ibm.com" <zohar@linux.ibm.com>,
        "yamada.masahiro@socionext.com" <yamada.masahiro@socionext.com>,
        "nayna@linux.ibm.com" <nayna@linux.ibm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
References: <157262960837.2838.17520432516398899751.stgit@naples-babu.amd.com>
 <157262962352.2838.15656190309312238595.stgit@naples-babu.amd.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Mon, 4 Nov 2019 12:54:00 +0100
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On 01/11/19 18:33, Moger, Babu wrote:
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 4153ca8cddb7..79abbdeca148 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -2533,6 +2533,11 @@ static void svm_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
>  {
>  }
>  
> +static bool svm_umip_emulated(void)
> +{
> +	return boot_cpu_has(X86_FEATURE_UMIP);
> +}

For hardware that supports UMIP, this is only needed because of your
patch 1.  Without it, X86_FEATURE_UMIP should already be enabled on
processors that natively support UMIP.

If you want UMIP *emulation* instead, this should become "return true".

>  static void update_cr0_intercept(struct vcpu_svm *svm)
>  {
>  	ulong gcr0 = svm->vcpu.arch.cr0;
> @@ -4438,6 +4443,13 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
>  	return 1;
>  }
>  
> +static int umip_interception(struct vcpu_svm *svm)
> +{
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +
> +	return kvm_emulate_instruction(vcpu, 0);
> +}
> +
>  static int pause_interception(struct vcpu_svm *svm)
>  {
>  	struct kvm_vcpu *vcpu = &svm->vcpu;
> @@ -4775,6 +4787,10 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
>  	[SVM_EXIT_SMI]				= nop_on_interception,
>  	[SVM_EXIT_INIT]				= nop_on_interception,
>  	[SVM_EXIT_VINTR]			= interrupt_window_interception,
> +	[SVM_EXIT_IDTR_READ]			= umip_interception,
> +	[SVM_EXIT_GDTR_READ]			= umip_interception,
> +	[SVM_EXIT_LDTR_READ]			= umip_interception,
> +	[SVM_EXIT_TR_READ]			= umip_interception,

This is missing enabling the intercepts.  Also, this can be just
emulate_on_interception instead of a new function.

Paolo

>  	[SVM_EXIT_RDPMC]			= rdpmc_interception,
>  	[SVM_EXIT_CPUID]			= cpuid_interception,
>  	[SVM_EXIT_IRET]                         = iret_interception,
> @@ -5976,11 +5992,6 @@ static bool svm_xsaves_supported(void)
>  	return boot_cpu_has(X86_FEATURE_XSAVES);
>  }
>  
> -static bool svm_umip_emulated(void)
> -{
> -	return false;
> -}
> -
>  static bool svm_pt_supported(void)
>  {
>  	return false;
>