On Fri, Apr 27, 2018 at 07:44:07AM +0000, Tian, Kevin wrote: > > From: Peter Xu [mailto:pet...@redhat.com] > > Sent: Friday, April 27, 2018 3:28 PM > > > > On Fri, Apr 27, 2018 at 07:02:14AM +0000, Tian, Kevin wrote: > > > > From: Jason Wang [mailto:jasow...@redhat.com] > > > > Sent: Friday, April 27, 2018 2:08 PM > > > > > > > > On 2018年04月25日 12:51, Peter Xu wrote: > > > > > For each VTDAddressSpace, now we maintain what IOVA ranges we > > have > > > > > mapped and what we have not. With that information, now we only > > > > send > > > > > MAP or UNMAP when necessary. Say, we don't send MAP notifies if > > we > > > > know > > > > > we have already mapped the range, meanwhile we don't send > > UNMAP > > > > notifies > > > > > if we know we never mapped the range at all. > > > > > > > > > > Signed-off-by: Peter Xu <pet...@redhat.com> > > > > > --- > > > > > include/hw/i386/intel_iommu.h | 2 ++ > > > > > hw/i386/intel_iommu.c | 28 ++++++++++++++++++++++++++++ > > > > > hw/i386/trace-events | 2 ++ > > > > > 3 files changed, 32 insertions(+) > > > > > > > > > > diff --git a/include/hw/i386/intel_iommu.h > > > > b/include/hw/i386/intel_iommu.h > > > > > index 486e205e79..09a2e94404 100644 > > > > > --- a/include/hw/i386/intel_iommu.h > > > > > +++ b/include/hw/i386/intel_iommu.h > > > > > @@ -27,6 +27,7 @@ > > > > > #include "hw/i386/ioapic.h" > > > > > #include "hw/pci/msi.h" > > > > > #include "hw/sysbus.h" > > > > > +#include "qemu/interval-tree.h" > > > > > > > > > > #define TYPE_INTEL_IOMMU_DEVICE "intel-iommu" > > > > > #define INTEL_IOMMU_DEVICE(obj) \ > > > > > @@ -95,6 +96,7 @@ struct VTDAddressSpace { > > > > > QLIST_ENTRY(VTDAddressSpace) next; > > > > > /* Superset of notifier flags that this address space has */ > > > > > IOMMUNotifierFlag notifier_flags; > > > > > + ITTree *iova_tree; /* Traces mapped IOVA ranges */ > > > > > }; > > > > > > > > > > struct VTDBus { > > > > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c > > > > > index a19c18b8d4..8f396a5d13 100644 > > > > > --- a/hw/i386/intel_iommu.c > > > > > +++ b/hw/i386/intel_iommu.c > > > > > @@ -768,12 +768,37 @@ typedef struct { > > > > > static int vtd_page_walk_one(IOMMUTLBEntry *entry, int level, > > > > > vtd_page_walk_info *info) > > > > > { > > > > > + VTDAddressSpace *as = info->as; > > > > > vtd_page_walk_hook hook_fn = info->hook_fn; > > > > > void *private = info->private; > > > > > + ITRange *mapped = it_tree_find(as->iova_tree, entry->iova, > > > > > + entry->iova + entry->addr_mask); > > > > > > > > > > assert(hook_fn); > > > > > + > > > > > + /* Update local IOVA mapped ranges */ > > > > > + if (entry->perm) { > > > > > + if (mapped) { > > > > > + /* Skip since we have already mapped this range */ > > > > > + trace_vtd_page_walk_one_skip_map(entry->iova, entry- > > > > >addr_mask, > > > > > + mapped->start, > > > > > mapped->end); > > > > > + return 0; > > > > > + } > > > > > + it_tree_insert(as->iova_tree, entry->iova, > > > > > + entry->iova + entry->addr_mask); > > > > > > > > I was consider a case e.g: > > > > > > > > 1) map A (iova) to B (pa) > > > > 2) invalidate A > > > > 3) map A (iova) to C (pa) > > > > 4) invalidate A > > > > > > > > In this case, we will probably miss a walk here. But I'm not sure it was > > > > allowed by the spec (though I think so). > > > > > > > > Hi, Kevin, > > > > Thanks for joining the discussion. > > > > > > > > I thought it was wrong in a glimpse, but then changed my mind after > > > another thinking. As long as device driver can quiescent the device > > > to not access A (iova) within above window, then above sequence > > > has no problem since any stale mappings (A->B) added before step 4) > > > won't be used and then will get flushed after step 4). Regarding to > > > that actually the 1st invalidation can be skipped: > > > > > > 1) map A (iova) to B (pa) > > > 2) driver programs device to use A > > > 3) driver programs device to not use A > > > 4) map A (iova) to C (pa) > > > A->B may be still valid in IOTLB > > > 5) invalidate A > > > 6) driver programs device to use A > > > > Note that IMHO this is a bit different from Jason's example, and it'll > > be fine. Current code should work well with this scenario since the > > emulation code will not aware of the map A until step (5). Then we'll > > have the correct mapping. > > you are right. we still need the extra PSI otherwise the 1st mapping > is problematic for use. So back to Jason's example. > > > > > While for Jason's example it's exactly the extra PSI that might cause > > stale mappings (though again I think it's still problematic...). > > problematic in software side (e.g. that way IOMMU core relies on > device drivers which conflict with the value of using IOMMU) but > it is OK from hardware p.o.v. btw the extra PSI itself doesn't cause > stale mapping. Instead it is device activity after that PSI may cause it. > > > > > Actually I think I can just fix up the code even if Jason's case > > happens by unmapping that first then remap: > > > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c > > index 31e9b52452..2a9584f9d8 100644 > > --- a/hw/i386/intel_iommu.c > > +++ b/hw/i386/intel_iommu.c > > @@ -778,13 +778,21 @@ static int vtd_page_walk_one(IOMMUTLBEntry > > *entry, int level, > > /* Update local IOVA mapped ranges */ > > if (entry->perm) { > > if (mapped) { > > - /* Skip since we have already mapped this range */ > > - trace_vtd_page_walk_one_skip_map(entry->iova, entry- > > >addr_mask, > > - mapped->start, mapped->end); > > - return 0; > > + int ret; > > + /* Cache the write permission */ > > + IOMMUAccessFlags flags = entry->perm; > > + > > + /* UNMAP the old first then remap. No need to touch IOVA tree > > */ > > + entry->perm = IOMMU_NONE; > > + ret = hook_fn(entry, private); > > + if (ret) { > > + return ret; > > + } > > + entry->perm = flags; > > + } else { > > + it_tree_insert(as->iova_tree, entry->iova, > > + entry->iova + entry->addr_mask); > > } > > - it_tree_insert(as->iova_tree, entry->iova, > > - entry->iova + entry->addr_mask); > > } else { > > if (!mapped) { > > /* Skip since we didn't map this range at all */ > > > > If we really think it necessary, I can squash this in, though this is > > a bit ugly. But I just want to confirm whether this would be anything > > we want... > > > > I didn’t look into your actual code yet. If others think above > change is OK then it's definitely good as we conform to hardware > behavior here. Otherwise if there is a way to detect such unusual > usage and then adopt some action (say kill the VM), it's also fine > since user knows he runs a bad OS which is not supported by > Qemu. It's just not good if such situation is not handled, which > leads to some undefined behavior which nobody knows the reason > w/o hard debug into. :-)
Yeah, then let me do this. :) Jason, would you be good with above change squashed? Thanks, -- Peter Xu