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

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Date:   Sun, 21 Jul 2019 13:57:41 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     "Singh, Brijesh" <brijesh.singh@....com>
cc:     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 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?

> @@ -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()?