linux-kernel - Re: [RFC PATCH] virtio: make sure legacy pci device gain 32bit-pfn vq

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Date:   Wed, 8 Dec 2021 06:08:58 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     王贇 <yun.wang@...ux.alibaba.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        "open list:VIRTIO CORE AND NET DRIVERS" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] virtio: make sure legacy pci device gain 32bit-pfn vq

On Wed, Dec 08, 2021 at 04:04:19PM +0800, 王贇 wrote:
> 
> 
> 在 2021/12/8 下午3:23, Michael S. Tsirkin 写道:
> > On Tue, Dec 07, 2021 at 05:09:56PM +0800, 王贇 wrote:
> > > 
> > > 
> > > 在 2021/12/7 下午4:13, Michael S. Tsirkin 写道:
> > > > On Tue, Dec 07, 2021 at 03:51:45PM +0800, 王贇 wrote:
> > > > > We observed issues like:
> > > > >     virtio-pci 0000:14:00.0: platform bug: legacy virtio-mmio must
> > > > >     not be used with RAM above 0x4000GB
> > > > > 
> > > > > when we have a legacy pci device which desired 32bit-pfn vq
> > > > > but gain 64bit-pfn instead, lead into the failure of probe.
> > > > > 
> > > > > vring_use_dma_api() is playing the key role in here, to help the
> > > > > allocation process understand which kind of vq it should alloc,
> > > > > however, it failed to take care the legacy pci device, which only
> > > > > have 32bit feature flag and can never have VIRTIO_F_ACCESS_PLATFORM
> > > > > setted.
> > > > > 
> > > > > This patch introduce force_dma flag to help vring_use_dma_api()
> > > > > understanding the requirement better, to avoid the failing.
> > > > > 
> > > > > Signed-off-by: Michael Wang <yun.wang@...ux.alibaba.com>
> > > > 
> > > > This will break configs where the device appears behind
> > > > a virtual iommu, so this won't fly.
> > > > Just make your device support 1.0, eh?
> > > 
> > > Hi, Michael
> > > 
> > > Thanks for the comment, unfortunately modify device is not an option for us
> > > :-(
> > > 
> > > Is there any idea on how to solve this issue properly?
> > > 
> > > Regards,
> > > Michael Wang
> > 
> > By the way, there is a bug in the error message. Want to fix that?
> 
> Could you please provide more detail about the bug? We'd like to help fixing
> it :-)

virtio-pci 0000:14:00.0: platform bug: legacy virtio-mmio must ...

should be virtio-pci not virtio-mmio



> Besides, I've checked that patch but it can't address our issue, we actually
> have this legacy pci device on arm platform, and the memory layout is
> unfriendly since allocation rarely providing page-address below 44bit, we
> understand the virtio-iommu case should not do force dma, while we don't
> have that so it's just working fine.
> 
> Regards,
> Michael Wang

Hmm wait a sec is it a physical device or a hypervisor?
If a physical one then doesn't it need VIRTIO_F_ORDER_PLATFORM
on ARM?



> > 
> > 
> > > > 
> > > > > ---
> > > > >    drivers/virtio/virtio_pci_legacy.c | 10 ++++++++++
> > > > >    drivers/virtio/virtio_ring.c       |  3 +++
> > > > >    include/linux/virtio.h             |  1 +
> > > > >    3 files changed, 14 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/virtio/virtio_pci_legacy.c
> > > > > b/drivers/virtio/virtio_pci_legacy.c
> > > > > index d62e983..11f2ebf 100644
> > > > > --- a/drivers/virtio/virtio_pci_legacy.c
> > > > > +++ b/drivers/virtio/virtio_pci_legacy.c
> > > > > @@ -263,6 +263,16 @@ int virtio_pci_legacy_probe(struct virtio_pci_device
> > > > > *vp_dev)
> > > > >    	vp_dev->setup_vq = setup_vq;
> > > > >    	vp_dev->del_vq = del_vq;
> > > > > 
> > > > > +	/*
> > > > > +	 * The legacy pci device requre 32bit-pfn vq,
> > > > > +	 * or setup_vq() will failed.
> > > > > +	 *
> > > > > +	 * Thus we make sure vring_use_dma_api() will
> > > > > +	 * return true during the allocation by marking
> > > > > +	 * force_dma here.
> > > > > +	 */
> > > > > +	vp_dev->vdev.force_dma = true;
> > > > > +
> > > > >    	return 0;
> > > > > 
> > > > >    err_iomap:
> > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > > index 3035bb6..6562e01 100644
> > > > > --- a/drivers/virtio/virtio_ring.c
> > > > > +++ b/drivers/virtio/virtio_ring.c
> > > > > @@ -245,6 +245,9 @@ static inline bool virtqueue_use_indirect(struct
> > > > > virtqueue *_vq,
> > > > > 
> > > > >    static bool vring_use_dma_api(struct virtio_device *vdev)
> > > > >    {
> > > > > +	if (vdev->force_dma)
> > > > > +		return true;
> > > > > +
> > > > >    	if (!virtio_has_dma_quirk(vdev))
> > > > >    		return true;
> > > > > 
> > > > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > > > > index 41edbc0..a4eb29d 100644
> > > > > --- a/include/linux/virtio.h
> > > > > +++ b/include/linux/virtio.h
> > > > > @@ -109,6 +109,7 @@ struct virtio_device {
> > > > >    	bool failed;
> > > > >    	bool config_enabled;
> > > > >    	bool config_change_pending;
> > > > > +	bool force_dma;
> > > > >    	spinlock_t config_lock;
> > > > >    	spinlock_t vqs_list_lock; /* Protects VQs list access */
> > > > >    	struct device dev;
> > > > > -- 
> > > > > 1.8.3.1