Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: iGdI+DcKJHsCT4DH16t9LU1f0E7Kfw2dDra2E61iictBCeQELuiGvuORiL5K164J3ShPiF9T+i
 Y6Cxu2yMue7w==
IronPort-SDR: stvAu5V5ArIkhb65+5xX22vrNhwq9qvEre1+vJPC+dd8YMhN4ZwLklfbXK9J9x0T9beEC2KXf+
 UDk1DR+bwfQA==
Date:   Tue, 6 Oct 2020 09:12:00 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     Vivek Goyal <vgoyal@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        virtio-fs-list <virtio-fs@redhat.com>, pbonzini@redhat.com
Subject: Re: [PATCH v4] kvm,x86: Exit to user space in case page fault error
Message-ID: <20201006161200.GB17610@linux.intel.com>
References: <20201002200214.GB10232@redhat.com>
 <20201002211314.GE24460@linux.intel.com>
 <20201005153318.GA4302@redhat.com>
 <20201005161620.GC11938@linux.intel.com>
 <20201006134629.GB5306@redhat.com>
 <877ds38n6r.fsf@vitty.brq.redhat.com>
 <20201006141501.GC5306@redhat.com>
 <874kn78l2z.fsf@vitty.brq.redhat.com>
 <20201006150817.GD5306@redhat.com>
 <871rib8ji1.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <871rib8ji1.fsf@vitty.brq.redhat.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Precedence: bulk

On Tue, Oct 06, 2020 at 05:24:54PM +0200, Vitaly Kuznetsov wrote:
> Vivek Goyal <vgoyal@redhat.com> writes:
> > So you will have to report token (along with -EFAULT) to user space. So this
> > is basically the 3rd proposal which is extension of kvm API and will
> > report say HVA/GFN also to user space along with -EFAULT.
> 
> Right, I meant to say that guest kernel has full register state of the
> userspace process which caused APF to get queued and instead of trying
> to extract it in KVM and pass to userspace in case of a (later) failure
> we limit KVM api change to contain token or GFN only and somehow keep
> the rest in the guest. This should help with TDX/SEV-ES.

Whatever gets reported to userspace should be identical with and without
async page faults, i.e. it definitely shouldn't have token information.

Note, TDX doesn't allow injection exceptions, so reflecting a #PF back
into the guest is not an option.  Nor do I think that's "correct"
behavior (see everyone's objections to using #PF for APF fixed).  I.e. the
event should probably be an IRQ.