linux-kernel - Re: [PATCH v10 08/16] KVM: X86: Introduce KVM_HC_PAGE_ENC

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Date:   Thu, 4 Feb 2021 10:03:14 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Ashish Kalra <Ashish.Kalra@....com>, pbonzini@...hat.com
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        rkrcmar@...hat.com, joro@...tes.org, bp@...e.de, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        srutherford@...gle.com, seanjc@...gle.com,
        venu.busireddy@...cle.com, brijesh.singh@....com
Subject: Re: [PATCH v10 08/16] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS
 hypercall

On 2/3/21 6:38 PM, Ashish Kalra wrote:
> From: Brijesh Singh <brijesh.singh@....com>
> 
> This hypercall is used by the SEV guest to notify a change in the page
> encryption status to the hypervisor. The hypercall should be invoked
> only when the encryption attribute is changed from encrypted -> decrypted
> and vice versa. By default all guest pages are considered encrypted.
> 
> The patch introduces a new shared pages list implemented as a
> sorted linked list to track the shared/unencrypted regions marked by the
> guest hypercall.
> 

...

> +
> +	if (enc) {
> +		ret = remove_shared_region(gfn_start, gfn_end,
> +					   &sev->shared_pages_list);
> +		if (ret != -ENOMEM)
> +			sev->shared_pages_list_count += ret;
> +	} else {
> +		ret = add_shared_region(gfn_start, gfn_end,
> +					&sev->shared_pages_list);
> +		if (ret > 0)
> +			sev->shared_pages_list_count++;
> +	}

I would move the shared_pages_list_count updates into the add/remove 
functions and then just return 0 or a -EXXXX error code from those 
functions. It seems simpler than "adding" ret or checking for a greater 
than 0 return code.

Thanks,
Tom

> +
> +	mutex_unlock(&kvm->lock);
> +	return ret;
> +}
> +
>   int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>   {
>   	struct kvm_sev_cmd sev_cmd;
> @@ -1693,6 +1842,7 @@ void sev_vm_destroy(struct kvm *kvm)
>   
>   	sev_unbind_asid(kvm, sev->handle);
>   	sev_asid_free(sev->asid);
> +	sev->shared_pages_list_count = 0;
>   }
>   
>   void __init sev_hardware_setup(void)
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index f923e14e87df..bb249ec625fc 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4536,6 +4536,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
>   	.complete_emulated_msr = svm_complete_emulated_msr,
>   
>   	.vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector,
> +
> +	.page_enc_status_hc = svm_page_enc_status_hc,
>   };
>   
>   static struct kvm_x86_init_ops svm_init_ops __initdata = {
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 0fe874ae5498..6437c1fa1f24 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -79,6 +79,9 @@ struct kvm_sev_info {
>   	unsigned long pages_locked; /* Number of pages locked */
>   	struct list_head regions_list;  /* List of registered regions */
>   	u64 ap_jump_table;	/* SEV-ES AP Jump Table address */
> +	/* List and count of shared pages */
> +	int shared_pages_list_count;
> +	struct list_head shared_pages_list;
>   };
>   
>   struct kvm_svm {
> @@ -472,6 +475,8 @@ int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
>   			       bool has_error_code, u32 error_code);
>   int nested_svm_exit_special(struct vcpu_svm *svm);
>   void sync_nested_vmcb_control(struct vcpu_svm *svm);
> +int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa,
> +			   unsigned long npages, unsigned long enc);
>   
>   extern struct kvm_x86_nested_ops svm_nested_ops;
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index cc60b1fc3ee7..bcbf53851612 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7705,6 +7705,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
>   	.can_emulate_instruction = vmx_can_emulate_instruction,
>   	.apic_init_signal_blocked = vmx_apic_init_signal_blocked,
>   	.migrate_timers = vmx_migrate_timers,
> +	.page_enc_status_hc = NULL,
>   
>   	.msr_filter_changed = vmx_msr_filter_changed,
>   	.complete_emulated_msr = kvm_complete_insn_gp,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 76bce832cade..2f17f0f9ace7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8162,6 +8162,12 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>   		kvm_sched_yield(vcpu->kvm, a0);
>   		ret = 0;
>   		break;
> +	case KVM_HC_PAGE_ENC_STATUS:
> +		ret = -KVM_ENOSYS;
> +		if (kvm_x86_ops.page_enc_status_hc)
> +			ret = kvm_x86_ops.page_enc_status_hc(vcpu->kvm,
> +					a0, a1, a2);
> +		break;
>   	default:
>   		ret = -KVM_ENOSYS;
>   		break;
> diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
> index 8b86609849b9..847b83b75dc8 100644
> --- a/include/uapi/linux/kvm_para.h
> +++ b/include/uapi/linux/kvm_para.h
> @@ -29,6 +29,7 @@
>   #define KVM_HC_CLOCK_PAIRING		9
>   #define KVM_HC_SEND_IPI		10
>   #define KVM_HC_SCHED_YIELD		11
> +#define KVM_HC_PAGE_ENC_STATUS		12
>   
>   /*
>    * hypercalls use architecture specific
>