linux-kernel - Re: [RFC PATCH 22/35] KVM: SVM: Add support for CR0 write traps for an SEV-ES guest

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Date:   Tue, 15 Sep 2020 10:56:29 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [RFC PATCH 22/35] KVM: SVM: Add support for CR0 write traps for
 an SEV-ES guest

On 9/14/20 5:13 PM, Sean Christopherson wrote:
> On Mon, Sep 14, 2020 at 03:15:36PM -0500, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@....com>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index b65bd0c986d4..6f5988c305e1 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -799,11 +799,29 @@ bool pdptrs_changed(struct kvm_vcpu *vcpu)
>>  }
>>  EXPORT_SYMBOL_GPL(pdptrs_changed);
>>  
>> +static void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0,
>> +			     unsigned long cr0)
> 
> What about using __kvm_set_cr*() instead of kvm_post_set_cr*()?  That would
> show that __kvm_set_cr*() is a subordinate of kvm_set_cr*(), and from the
> SVM side would provide the hint that the code is skipping the front end of
> kvm_set_cr*().

Ok, I'll change this (and the others) to __kvm_set_cr* and export them.

> 
>> +{
>> +	unsigned long update_bits = X86_CR0_PG | X86_CR0_WP;
>> +
>> +	if ((cr0 ^ old_cr0) & X86_CR0_PG) {
>> +		kvm_clear_async_pf_completion_queue(vcpu);
>> +		kvm_async_pf_hash_reset(vcpu);
>> +	}
>> +
>> +	if ((cr0 ^ old_cr0) & update_bits)
>> +		kvm_mmu_reset_context(vcpu);
>> +
>> +	if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
>> +	    kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
>> +	    !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
>> +		kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
>> +}
>> +
>>  int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>>  {
>>  	unsigned long old_cr0 = kvm_read_cr0(vcpu);
>>  	unsigned long pdptr_bits = X86_CR0_CD | X86_CR0_NW | X86_CR0_PG;
>> -	unsigned long update_bits = X86_CR0_PG | X86_CR0_WP;
>>  
>>  	cr0 |= X86_CR0_ET;
>>  
>> @@ -842,22 +860,23 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>>  
>>  	kvm_x86_ops.set_cr0(vcpu, cr0);
>>  
>> -	if ((cr0 ^ old_cr0) & X86_CR0_PG) {
>> -		kvm_clear_async_pf_completion_queue(vcpu);
>> -		kvm_async_pf_hash_reset(vcpu);
>> -	}
>> +	kvm_post_set_cr0(vcpu, old_cr0, cr0);
>>  
>> -	if ((cr0 ^ old_cr0) & update_bits)
>> -		kvm_mmu_reset_context(vcpu);
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_set_cr0);
>>  
>> -	if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
>> -	    kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
>> -	    !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
>> -		kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
>> +int kvm_track_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
> 
> I really dislike the "track" terminology.  For me, using "track" as the verb
> in a function implies the function activates tracking.  But it's probably a
> moot point, because similar to EFER, I don't see any reason to put the front
> end of the emulation into x86.c.  Both getting old_cr0 and setting
> vcpu->arch.cr0 can be done in svm.c

Yup, I can move that to svm.c.

Thanks,
Tom

> 
>> +{
>> +	unsigned long old_cr0 = kvm_read_cr0(vcpu);
>> +
>> +	vcpu->arch.cr0 = cr0;
>> +
>> +	kvm_post_set_cr0(vcpu, old_cr0, cr0);
>>  
>>  	return 0;
>>  }
>> -EXPORT_SYMBOL_GPL(kvm_set_cr0);
>> +EXPORT_SYMBOL_GPL(kvm_track_cr0);
>>  
>>  void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
>>  {
>> -- 
>> 2.28.0
>>