linux-kernel - Re: [PATCH v8 1/2] virtio: let arch validate VIRTIO features

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Message-ID: <20200819113446.3f098d1e.cohuck@redhat.com>
Date:   Wed, 19 Aug 2020 11:34:46 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, pasic@...ux.ibm.com,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, mst@...hat.com,
        jasowang@...hat.com, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, thomas.lendacky@....com,
        david@...son.dropbear.id.au, linuxram@...ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v8 1/2] virtio: let arch validate VIRTIO features

On Wed, 19 Aug 2020 10:50:18 +0200
Pierre Morel <pmorel@...ux.ibm.com> wrote:

> On 2020-08-18 19:19, Cornelia Huck wrote:
> > On Tue, 18 Aug 2020 16:58:30 +0200
> > Pierre Morel <pmorel@...ux.ibm.com> wrote:
> >   
> ...
> >> +config ARCH_HAS_RESTRICTED_MEMORY_ACCESS
> >> +	bool
> >> +	help
> >> +	  This option is selected by any architecture enforcing
> >> +	  VIRTIO_F_IOMMU_PLATFORM  
> > 
> > This option is only for a very specific case of "restricted memory
> > access", namely the kind that requires IOMMU_PLATFORM for virtio
> > devices. ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS? Or is this intended
> > to cover cases outside of virtio as well?  
> 
> AFAIK we did not identify other restrictions so adding VIRTIO in the 
> name should be the best thing to do.
> 
> If new restrictions appear they also may be orthogonal.
> 
> I will change to ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS if no one 
> complains.
> 
> >   
> >> +
> >>   menuconfig VIRTIO_MENU
> >>   	bool "Virtio drivers"
> >>   	default y
> >> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> >> index a977e32a88f2..1471db7d6510 100644
> >> --- a/drivers/virtio/virtio.c
> >> +++ b/drivers/virtio/virtio.c
> >> @@ -176,6 +176,10 @@ int virtio_finalize_features(struct virtio_device *dev)
> >>   	if (ret)
> >>   		return ret;
> >>   
> >> +	ret = arch_has_restricted_memory_access(dev);
> >> +	if (ret)
> >> +		return ret;  
> > 
> > Hm, I'd rather have expected something like
> > 
> > if (arch_has_restricted_memory_access(dev)) {  
> 
> may be also change the callback name to
> arch_has_restricted_virtio_memory_access() ?

Yes, why not.

> 
> > 	// enforce VERSION_1 and IOMMU_PLATFORM
> > }
> > 
> > Otherwise, you're duplicating the checks in the individual architecture
> > callbacks again.  
> 
> Yes, I agree and go back this way.
> 
> > 
> > [Not sure whether the device argument would be needed here; are there
> > architectures where we'd only require IOMMU_PLATFORM for a subset of
> > virtio devices?]  
> 
> I don't think so and since we do the checks locally, we do not need the 
> device argument anymore.

Yes, that would also remove some layering entanglement.