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Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ran
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges |
Date: |
Fri, 27 Apr 2018 15:28:10 +0800 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Fri, Apr 27, 2018 at 07:02:14AM +0000, Tian, Kevin wrote:
> > From: Jason Wang [mailto:address@hidden
> > 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 <address@hidden>
> > > ---
> > > 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.
While for Jason's example it's exactly the extra PSI that might cause
stale mappings (though again I think it's still problematic...).
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...
Thanks,
--
Peter Xu
- [Qemu-devel] [PATCH 05/10] intel-iommu: introduce vtd_page_walk_info, (continued)
- [Qemu-devel] [PATCH 05/10] intel-iommu: introduce vtd_page_walk_info, Peter Xu, 2018/04/25
- [Qemu-devel] [PATCH 06/10] intel-iommu: pass in address space when page walk, Peter Xu, 2018/04/25
- [Qemu-devel] [PATCH 04/10] intel-iommu: only do page walk for MAP notifiers, Peter Xu, 2018/04/25
- [Qemu-devel] [PATCH 07/10] util: implement simple interval tree logic, Peter Xu, 2018/04/25
- [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Peter Xu, 2018/04/25
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Jason Wang, 2018/04/27
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Peter Xu, 2018/04/27
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Tian, Kevin, 2018/04/27
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges,
Peter Xu <=
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Tian, Kevin, 2018/04/27
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Peter Xu, 2018/04/27
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Peter Xu, 2018/04/27
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Tian, Kevin, 2018/04/27
- Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges, Jason Wang, 2018/04/27
[Qemu-devel] [PATCH 09/10] intel-iommu: don't unmap all for shadow page table, Peter Xu, 2018/04/25
[Qemu-devel] [PATCH 10/10] intel-iommu: remove notify_unmap for page walk, Peter Xu, 2018/04/25
Re: [Qemu-devel] [PATCH 00/10] intel-iommu: nested vIOMMU, cleanups, bug fixes, no-reply, 2018/04/25