linux-kernel - Re: [PATCH 2/3] KVM, SEV: Add support for SEV local migration

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Date:   Mon, 12 Jul 2021 16:09:14 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Peter Gonda <pgonda@...gle.com>, kvm@...r.kernel.org
Cc:     brijesh.singh@....com, Lars Bull <larsbull@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] KVM, SEV: Add support for SEV local migration



On 6/21/21 11:31 AM, Peter Gonda wrote:

> +	if (!sev_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (sev->es_active)
> +		return -EPERM;
> +
> +	if (sev->info_token != 0)
> +		return -EEXIST;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +			   sizeof(params)))
> +		return -EFAULT;
> +
> +	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> +	if (!entry)
> +		return -ENOMEM;
> +
> +	entry->asid = sev->asid;
> +	entry->handle = sev->handle;
> +	entry->pages_locked = sev->pages_locked;
> +	entry->misc_cg = sev->misc_cg;
> +
> +	INIT_LIST_HEAD(&entry->regions_list);
> +	list_replace_init(&sev->regions_list, &entry->regions_list);

I believe the entry->regions_list will be NULL if the command is called 
before the memory regions are registered. The quesiton is, do you need 
to check whether for a valid sev->handle (i.e, LAUNCH_START is done)?


> +
>   /* Userspace wants to query session length. */
>   static int
>   __sev_send_start_query_session_length(struct kvm *kvm, struct kvm_sev_cmd *argp,
> @@ -1513,6 +1711,18 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>   		goto out;
>   	}
>   
> +	/*
> +	 * If this VM has started exporting its SEV contents to another VM,
> +	 * it's not allowed to do any more SEV operations that may modify the
> +	 * SEV state.
> +	 */
> +	if (to_kvm_svm(kvm)->sev_info.info_token &&
> +	    sev_cmd.id != KVM_SEV_DBG_ENCRYPT &&
> +	    sev_cmd.id != KVM_SEV_DBG_DECRYPT) {
> +		r = -EPERM;
> +		goto out;
> +	}

Maybe move this check in a function so that it can later extended for 
SEV-SNP (cmd ids for the debug is different).

Something like:

static bool is_local_mig_active(struct kvm *)
{
	....
}

Once the migration range hypercall is merged, we also need to preserve 
any metadata memory maintained by KVM for the unencrypted ranges.

-Brijesh