linux-kernel - Re: [PATCH 2/2] iommu/virtio: Add ops->flush_iotlb

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Message-ID: <ba38b6d90e1f24f249ed8a18e65c403be6ff90e9.camel@linux.ibm.com>
Date:   Wed, 06 Sep 2023 09:55:49 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        virtualization@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iommu/virtio: Add ops->flush_iotlb_all and enable
 deferred flush

On Mon, 2023-09-04 at 17:33 +0100, Robin Murphy wrote:
> On 2023-09-04 16:34, Jean-Philippe Brucker wrote:
> > On Fri, Aug 25, 2023 at 05:21:26PM +0200, Niklas Schnelle wrote:
> > > Add ops->flush_iotlb_all operation to enable virtio-iommu for the
> > > dma-iommu deferred flush scheme. This results inn a significant increase
> > 
> > in
> > 
> > > in performance in exchange for a window in which devices can still
> > > access previously IOMMU mapped memory. To get back to the prior behavior
> > > iommu.strict=1 may be set on the kernel command line.
> > 
> > Maybe add that it depends on CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT} as
> > well, because I've seen kernel configs that enable either.
> 
> Indeed, I'd be inclined phrase it in terms of the driver now actually 
> being able to honour lazy mode when requested (which happens to be the 
> default on x86), rather than as if it might be some 
> potentially-unexpected change in behaviour.
> 
> Thanks,
> Robin.

I kept running this series on a KVM guest on my private workstation
(QEMU v8.0.4) and while running iperf3 on a passed-through Intel 82599
VF. I got a bunch of IOMMU events similar to the following as well as
card resets in the host.

..
[ 5959.338214] vfio-pci 0000:04:10.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0037 address=0x7b657064 flags=0x0000]
[ 5963.353429] ixgbe 0000:03:00.0 enp3s0: Detected Tx Unit Hang
                 Tx Queue             <0>
                 TDH, TDT             <93>, <9d>
                 next_to_use          <9d>
                 next_to_clean        <93>
               tx_buffer_info[next_to_clean]
                 time_stamp           <10019e800>
                 jiffies              <10019ec80>
...

I retested on v6.5 vanilla (guest & host) and still get the above
errors so luckily for me it doesn't seem to be caused by the new code
but I can't reproduce it without virtio-iommu. Any idea what could
cause this?


> 
> > > Link: https://lore.kernel.org/lkml/20230802123612.GA6142@myrica/
> > > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > > ---
> > >   drivers/iommu/virtio-iommu.c | 12 ++++++++++++
> > >   1 file changed, 12 insertions(+)
> > > 
> > > diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> > > index fb73dec5b953..1b7526494490 100644
> > > --- a/drivers/iommu/virtio-iommu.c
> > > +++ b/drivers/iommu/virtio-iommu.c
> > > @@ -924,6 +924,15 @@ static int viommu_iotlb_sync_map(struct iommu_domain *domain,
> > >   	return viommu_sync_req(vdomain->viommu);
> > >   }
> > >   
> > > +static void viommu_flush_iotlb_all(struct iommu_domain *domain)
> > > +{
> > > +	struct viommu_domain *vdomain = to_viommu_domain(domain);
> > > +
> > > +	if (!vdomain->nr_endpoints)
> > > +		return;
> > 
> > As for patch 1, a NULL check in viommu_sync_req() would allow dropping
> > this one
> > 
> > Thanks,
> > Jean

Right, makes sense will move the check into viommu_sync_req() and add a
coment that it is there fore the cases where viommu_iotlb_sync() et al
get called before the IOMMU is set up.

> > 
> > > +	viommu_sync_req(vdomain->viommu);
> > > +}
> > > +
> > >   static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
> > >   {
> > >   	struct iommu_resv_region *entry, *new_entry, *msi = NULL;
> > > @@ -1049,6 +1058,8 @@ static bool viommu_capable(struct device *dev, enum iommu_cap cap)
> > >   	switch (cap) {
> > >   	case IOMMU_CAP_CACHE_COHERENCY:
> > >   		return true;
> > > +	case IOMMU_CAP_DEFERRED_FLUSH:
> > > +		return true;
> > >   	default:
> > >   		return false;
> > >   	}
> > > @@ -1069,6 +1080,7 @@ static struct iommu_ops viommu_ops = {
> > >   		.map_pages		= viommu_map_pages,
> > >   		.unmap_pages		= viommu_unmap_pages,
> > >   		.iova_to_phys		= viommu_iova_to_phys,
> > > +		.flush_iotlb_all	= viommu_flush_iotlb_all,
> > >   		.iotlb_sync		= viommu_iotlb_sync,
> > >   		.iotlb_sync_map		= viommu_iotlb_sync_map,
> > >   		.free			= viommu_domain_free,
> > > 
> > > -- 
> > > 2.39.2
> > >