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

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Message-ID: <08c28615-e16e-fe5d-4f04-24ec39387c7d@redhat.com>
Date:   Mon, 30 Nov 2020 19:15:33 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        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 15/09/20 00:13, Sean Christopherson wrote:
>> +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*().

No, kvm_post_set_cr0 is exactly the right name because it doesn't set 
any state.  __kvm_set_cr0 tells me that it is a (rarely used) way to set 
CR0, which this function isn't.

Sorry Tom for not catching this earlier.

Paolo

>> +{
>> +	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);