Re: [RFC] KVM: x86: Support KVM VMs sharing SEV context
From: Steve Rutherford
Date: Wed Feb 24 2021 - 22:57:29 EST
On Wed, Feb 24, 2021 at 9:37 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> + unsigned int asid;
>
> + int ret;
>
> +
>
> + if (!sev_guest(kvm))
>
> + return -ENOTTY;
>
> +
>
> + mutex_lock(&kvm->lock);
>
> +
>
> + /* Mirrors of mirrors should work, but let's not get silly */
>
>
Do we really care?
Yes, unless you reparent mirrors of mirrors to the original ASID
owner. If you don't do that, I think userspace could pump a chain of
mirrors to blow the kernel stack when it closes the leaf vm, since you
could build up a chain of sev_vm_destroys. Refcounting the ASIDs
directly would also fix this.
Nate's early implementation did the reparenting, but I pushed for the
simplification since it made the locking a bit hairy.
>
>
> + if (is_mirroring_enc_context(kvm)) {
>
> + ret = -ENOTTY;
>
> + goto failed;
>
> + }
>
> +