linux-kernel - Re: [PATCH 2/4] kvm: svm: Enable UMIP feature on AMD

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Message-ID: <2f61ae5c-0658-e5c9-754c-9ca80148a54d@amd.com>
Date:   Mon, 4 Nov 2019 18:45:48 +0000
From:   "Moger, Babu" <Babu.Moger@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "zohar@...ux.ibm.com" <zohar@...ux.ibm.com>,
        "yamada.masahiro@...ionext.com" <yamada.masahiro@...ionext.com>,
        "nayna@...ux.ibm.com" <nayna@...ux.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH 2/4] kvm: svm: Enable UMIP feature on AMD



On 11/4/19 5:54 AM, Paolo Bonzini wrote:
> 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.

Yes, That is correct. Will remove the patch #1. Intention was to enable
UMIP for the hardware that supports it. Will send out only the config
changes(Patch #4).  Also there is a complexity with supporting emulation
on SEV guest.

> 
> 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;
>>
>