linux-kernel - Re: [PATCH v3 08/11] KVM: X86: Introduce KVM_HC_PAGE_ENC

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Message-ID: <8c4e2f4b-0153-3721-a8b3-4842d45cb1bf@amd.com>
Date:   Tue, 23 Jul 2019 15:16:50 +0000
From:   "Singh, Brijesh" <brijesh.singh@....com>
To:     David Rientjes <rientjes@...gle.com>
CC:     "Singh, Brijesh" <brijesh.singh@....com>,
        Cfir Cohen <cfir@...gle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...e.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 08/11] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS
 hypercall



On 7/21/19 3:57 PM, David Rientjes wrote:
> On Wed, 10 Jul 2019, Singh, Brijesh wrote:
> 
>> diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt
>> index da24c138c8d1..94f0611f4d88 100644
>> --- a/Documentation/virtual/kvm/hypercalls.txt
>> +++ b/Documentation/virtual/kvm/hypercalls.txt
>> @@ -141,3 +141,17 @@ a0 corresponds to the APIC ID in the third argument (a2), bit 1
>>   corresponds to the APIC ID a2+1, and so on.
>>   
>>   Returns the number of CPUs to which the IPIs were delivered successfully.
>> +
>> +7. KVM_HC_PAGE_ENC_STATUS
>> +-------------------------
>> +Architecture: x86
>> +Status: active
>> +Purpose: Notify the encryption status changes in guest page table (SEV guest)
>> +
>> +a0: the guest physical address of the start page
>> +a1: the number of pages
>> +a2: encryption attribute
>> +
>> +   Where:
>> +	* 1: Encryption attribute is set
>> +	* 0: Encryption attribute is cleared
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 26d1eb83f72a..b463a81dc176 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1199,6 +1199,8 @@ struct kvm_x86_ops {
>>   	uint16_t (*nested_get_evmcs_version)(struct kvm_vcpu *vcpu);
>>   
>>   	bool (*need_emulation_on_page_fault)(struct kvm_vcpu *vcpu);
>> +	int (*page_enc_status_hc)(struct kvm *kvm, unsigned long gpa,
>> +				  unsigned long sz, unsigned long mode);
>>   };
>>   
>>   struct kvm_arch_async_pf {
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 3089942f6630..431718309359 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -135,6 +135,8 @@ struct kvm_sev_info {
>>   	int fd;			/* SEV device fd */
>>   	unsigned long pages_locked; /* Number of pages locked */
>>   	struct list_head regions_list;  /* List of registered regions */
>> +	unsigned long *page_enc_bmap;
>> +	unsigned long page_enc_bmap_size;
>>   };
>>   
>>   struct kvm_svm {
>> @@ -1910,6 +1912,8 @@ static void sev_vm_destroy(struct kvm *kvm)
>>   
>>   	sev_unbind_asid(kvm, sev->handle);
>>   	sev_asid_free(kvm);
>> +
>> +	kvfree(sev->page_enc_bmap);
>>   }
>>   
>>   static void avic_vm_destroy(struct kvm *kvm)
> 
> Adding Cfir who flagged this kvfree().
> 
> Other freeing of sev->page_enc_bmap in this patch also set
> sev->page_enc_bmap_size to 0 and neither set sev->page_enc_bmap to NULL
> after freeing it.
> 
> For extra safety, is it possible to sev->page_enc_bmap = NULL anytime the
> bitmap is kvfreed?
> 

Good catch, I'll fix it in next rev.

>> @@ -2084,6 +2088,7 @@ static void avic_set_running(struct kvm_vcpu *vcpu, bool is_run)
>>   
>>   static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>   {
>> +	struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info;
>>   	struct vcpu_svm *svm = to_svm(vcpu);
>>   	u32 dummy;
>>   	u32 eax = 1;
>> @@ -2105,6 +2110,12 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>   
>>   	if (kvm_vcpu_apicv_active(vcpu) && !init_event)
>>   		avic_update_vapic_bar(svm, APIC_DEFAULT_PHYS_BASE);
>> +
>> +	/* reset the page encryption bitmap */
>> +	if (sev_guest(vcpu->kvm)) {
>> +		kvfree(sev->page_enc_bmap);
>> +		sev->page_enc_bmap_size = 0;
>> +	}
>>   }
>>   
>>   static int avic_init_vcpu(struct vcpu_svm *svm)
> 
> What is protecting sev->page_enc_bmap and sev->page_enc_bmap_size in calls
> to svm_vcpu_reset()?
> 

Yes, it need to be protected with vm lock. I will fix it in next rev.
Additionally, I think what I have here is wrong, we need to reset the
bitmap only when bsp is getting reset.

-Brijesh