From: Eugenio Perez Martin <eperezma@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
Yan Zhao <yan.y.zhao@intel.com>,
Juan Quintela <quintela@redhat.com>,
Jason Wang <jasowang@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
qemu-devel@nongnu.org, Eric Auger <eric.auger@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier
Date: Tue, 11 Aug 2020 19:10:09 +0200 [thread overview]
Message-ID: <CAJaqyWdbvS7+8f5d8jQjdmuVio+QvoFE77kNJNA1buaGsk_JAw@mail.gmail.com> (raw)
In-Reply-To: <CAJaqyWf5=fwwcgZgOdipt54mq=vPZkQLGp9xWRG7Tnw-E9xjCA@mail.gmail.com>
On Tue, Aug 11, 2020 at 7:01 PM Eugenio Perez Martin
<eperezma@redhat.com> wrote:
>
> On Fri, Jun 26, 2020 at 11:29 PM Peter Xu <peterx@redhat.com> wrote:
> >
> > Hi, Eugenio,
> >
> > (CCing Eric, Yan and Michael too)
> >
> > On Fri, Jun 26, 2020 at 08:41:22AM +0200, Eugenio Pérez wrote:
> > > diff --git a/memory.c b/memory.c
> > > index 2f15a4b250..7f789710d2 100644
> > > --- a/memory.c
> > > +++ b/memory.c
> > > @@ -1915,8 +1915,6 @@ void memory_region_notify_one(IOMMUNotifier *notifier,
> > > return;
> > > }
> > >
> > > - assert(entry->iova >= notifier->start && entry_end <= notifier->end);
> >
> > I can understand removing the assertion should solve the issue, however imho
> > the major issue is not about this single assertion but the whole addr_mask
> > issue behind with virtio...
> >
> > For normal IOTLB invalidations, we were trying our best to always make
> > IOMMUTLBEntry contain a valid addr_mask to be 2**N-1. E.g., that's what we're
> > doing with the loop in vtd_address_space_unmap().
> >
> > But this is not the first time that we may want to break this assumption for
> > virtio so that we make the IOTLB a tuple of (start, len), then that len can be
> > not a address mask any more. That seems to be more efficient for things like
> > vhost because iotlbs there are not page based, so it'll be inefficient if we
> > always guarantee the addr_mask because it'll be quite a lot more roundtrips of
> > the same range of invalidation. Here we've encountered another issue of
> > triggering the assertion with virtio-net, but only with the old RHEL7 guest.
> >
> > I'm thinking whether we can make the IOTLB invalidation configurable by
> > specifying whether the backend of the notifier can handle arbitary address
> > range in some way. So we still have the guaranteed addr_masks by default
> > (since I still don't think totally break the addr_mask restriction is wise...),
> > however we can allow the special backends to take adavantage of using arbitary
> > (start, len) ranges for reasons like performance.
> >
> > To do that, a quick idea is to introduce a flag IOMMU_NOTIFIER_ARBITRARY_MASK
> > to IOMMUNotifierFlag, to declare that the iommu notifier (and its backend) can
> > take arbitrary address mask, then it can be any value and finally becomes a
> > length rather than an addr_mask. Then for every iommu notify() we can directly
> > deliver whatever we've got from the upper layer to this notifier. With the new
> > flag, vhost can do iommu_notifier_init() with UNMAP|ARBITRARY_MASK so it
> > declares this capability. Then no matter for device iotlb or normal iotlb, we
> > skip the complicated procedure to split a big range into small ranges that are
> > with strict addr_mask, but directly deliver the message to the iommu notifier.
> > E.g., we can skip the loop in vtd_address_space_unmap() if the notifier is with
> > ARBITRARY flag set.
> >
> > Then, the assert() is not accurate either, and may become something like:
> >
> > diff --git a/memory.c b/memory.c
> > index 2f15a4b250..99d0492509 100644
> > --- a/memory.c
> > +++ b/memory.c
> > @@ -1906,6 +1906,7 @@ void memory_region_notify_one(IOMMUNotifier *notifier,
> > {
> > IOMMUNotifierFlag request_flags;
> > hwaddr entry_end = entry->iova + entry->addr_mask;
> > + IOMMUTLBEntry tmp = *entry;
> >
> > /*
> > * Skip the notification if the notification does not overlap
> > @@ -1915,7 +1916,13 @@ void memory_region_notify_one(IOMMUNotifier *notifier,
> > return;
> > }
> >
> > - assert(entry->iova >= notifier->start && entry_end <= notifier->end);
> > + if (notifier->notifier_flags & IOMMU_NOTIFIER_ARBITRARY_MASK) {
> > + tmp.iova = MAX(tmp.iova, notifier->start);
>
> Hi!
>
> If I modify the tmp.iova, the guest will complain (in dmesg):
> [ 154.426828] DMAR: DRHD: handling fault status reg 2
> [ 154.427700] DMAR: [DMA Read] Request device [01:00.0] fault addr
> ffff90d53fada000 [fault reason 04] Access beyond MGAW
>
> And will not forward packets anymore on that interface. Guests are
> totally ok if I only modify addr_mask.
>
> Still investigating the issue.
>
> Thanks!
>
Sorry it seems that I lost the nitpick Yan pointed out :).
Sending RFC v3.
>
> > + tmp.addr_mask = MIN(tmp.addr_mask, notifier->end);
> > + assert(tmp.iova <= tmp.addr_mask);
> > + } else {
> > + assert(entry->iova >= notifier->start && entry_end <= notifier->end);
> > + }
> >
> > if (entry->perm & IOMMU_RW) {
> > request_flags = IOMMU_NOTIFIER_MAP;
> > @@ -1924,7 +1931,7 @@ void memory_region_notify_one(IOMMUNotifier *notifier,
> > }
> >
> > if (notifier->notifier_flags & request_flags) {
> > - notifier->notify(notifier, entry);
> > + notifier->notify(notifier, &tmp);
> > }
> > }
> >
> > Then we can keep the assert() for e.g. vfio, however vhost can skip it and even
> > get some further performance boosts.. Does that make sense?
> >
> > Thanks,
> >
> > --
> > Peter Xu
> >
next prev parent reply other threads:[~2020-08-11 17:11 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-26 6:41 [RFC v2 0/1] memory: Delete assertion in memory_region_unregister_iommu_notifier Eugenio Pérez
2020-06-26 6:41 ` [RFC v2 1/1] " Eugenio Pérez
2020-06-26 21:29 ` Peter Xu
2020-06-27 7:26 ` Yan Zhao
2020-06-27 12:57 ` Peter Xu
2020-06-28 1:36 ` Yan Zhao
2020-06-28 7:03 ` Jason Wang
2020-06-28 14:47 ` Peter Xu
2020-06-29 5:51 ` Jason Wang
2020-06-29 13:34 ` Peter Xu
2020-06-30 2:41 ` Jason Wang
2020-06-30 8:29 ` Jason Wang
2020-06-30 9:21 ` Michael S. Tsirkin
2020-06-30 9:23 ` Jason Wang
2020-06-30 15:20 ` Peter Xu
2020-07-01 8:11 ` Jason Wang
2020-07-01 12:16 ` Peter Xu
2020-07-01 12:30 ` Jason Wang
2020-07-01 12:41 ` Peter Xu
2020-07-02 3:00 ` Jason Wang
2020-06-30 15:39 ` Peter Xu
2020-07-01 8:09 ` Jason Wang
2020-07-02 3:01 ` Jason Wang
2020-07-02 15:45 ` Peter Xu
2020-07-03 7:24 ` Jason Wang
2020-07-03 13:03 ` Peter Xu
2020-07-07 8:03 ` Jason Wang
2020-07-07 19:54 ` Peter Xu
2020-07-08 5:42 ` Jason Wang
2020-07-08 14:16 ` Peter Xu
2020-07-09 5:58 ` Jason Wang
2020-07-09 14:10 ` Peter Xu
2020-07-10 6:34 ` Jason Wang
2020-07-10 13:30 ` Peter Xu
2020-07-13 4:04 ` Jason Wang
2020-07-16 1:00 ` Peter Xu
2020-07-16 2:54 ` Jason Wang
2020-07-17 14:18 ` Peter Xu
2020-07-20 4:02 ` Jason Wang
2020-07-20 13:03 ` Peter Xu
2020-07-21 6:20 ` Jason Wang
2020-07-21 15:10 ` Peter Xu
2020-08-03 16:00 ` Eugenio Pérez
2020-08-04 20:30 ` Peter Xu
2020-08-05 5:45 ` Jason Wang
2020-08-11 17:01 ` Eugenio Perez Martin
2020-08-11 17:10 ` Eugenio Perez Martin [this message]
2020-06-29 15:05 ` [RFC v2 0/1] " Paolo Bonzini
2020-07-03 7:39 ` Eugenio Perez Martin
2020-07-03 10:10 ` Paolo Bonzini
2020-08-11 17:55 ` [RFC v3 " Eugenio Pérez
2020-08-11 17:55 ` [RFC v3 1/1] memory: Skip bad range assertion if notifier supports arbitrary masks Eugenio Pérez
2020-08-12 2:24 ` Jason Wang
2020-08-12 8:49 ` Eugenio Perez Martin
2020-08-18 14:24 ` Eugenio Perez Martin
2020-08-19 7:15 ` Jason Wang
2020-08-19 8:22 ` Eugenio Perez Martin
2020-08-19 9:36 ` Jason Wang
2020-08-19 15:50 ` Peter Xu
2020-08-20 2:28 ` Jason Wang
2020-08-21 14:12 ` Peter Xu
2020-09-01 3:05 ` Jason Wang
2020-09-01 19:35 ` Peter Xu
2020-09-02 5:13 ` Jason Wang
2020-08-11 18:10 ` [RFC v3 0/1] memory: Delete assertion in memory_region_unregister_iommu_notifier Eugenio Perez Martin
2020-08-11 19:27 ` Peter Xu
2020-08-12 14:33 ` Eugenio Perez Martin
2020-08-12 21:12 ` Peter Xu
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