From: "Xu, Quan" <quan.xu@intel.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
"Wu, Feng" <feng.wu@intel.com>,
George Dunlap <george.dunlap@eu.citrix.com>,
Liu Jinsong <jinsong.liu@alibaba-inc.com>,
Dario Faggioli <dario.faggioli@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
"Nakajima, Jun" <jun.nakajima@intel.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Keir Fraser <keir@xen.org>
Subject: Re: [PATCH 1/2] IOMMU/MMU: Adjust top level functions for VT-d Device-TLB flush error.
Date: Wed, 30 Mar 2016 02:28:13 +0000 [thread overview]
Message-ID: <945CA011AD5F084CBEA3E851C0AB28894B871005@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <56FA48E302000078000E0B40@prv-mh.provo.novell.com>
On March 29, 2016 3:21pm, <JBeulich@suse.com> wrote:
> >>> On 28.03.16 at 05:33, <quan.xu@intel.com> wrote:
> > On March 18, 2016 1:15am, <JBeulich@suse.com> wrote:
> >> >>> On 17.03.16 at 07:54, <quan.xu@intel.com> wrote:
> >> > --- a/xen/common/grant_table.c
> >> > +++ b/xen/common/grant_table.c
> >> > @@ -932,8 +932,9 @@ __gnttab_map_grant_ref(
> >> > {
> >> > nr_gets++;
> >> > (void)get_page(pg, rd);
> >> > - if ( !(op->flags & GNTMAP_readonly) )
> >> > - get_page_type(pg, PGT_writable_page);
> >> > + if ( !(op->flags & GNTMAP_readonly) &&
> >> > + !get_page_type(pg, PGT_writable_page) )
> >> > + goto could_not_pin;
> >>
> >> This needs explanation, as it doesn't look related to what your
> >> actual goal is: If an error was possible here, I think this would be
> >> a security issue. However, as also kind of documented by the
> >> explicitly ignored return value from get_page(), it is my understanding there
> here we only obtain an _extra_ reference.
> >>
> >
> > For this point, I inferred from:
> > map_vcpu_info()
> > {
> > ...
> > if ( !get_page_type(page, PGT_writable_page) )
> > {
> > put_page(page);
> > return -EINVAL;
> > }
> > ...
> > }
> > , then for get_page_type(), I think the return value:
> > 0 -- error,
> > 1-- right.
> >
> > So if get_page_type() is failed, we should goto could_not_pin.
>
> Did you read my reply at all? The explanation I'm expecting here is why error
> checking is all of the sudden needed _at all_.
>
Sorry for my stupid reply.
As in this version, before the open discussion, I try to return the iommu_{,un}map_page() error in this call tree:
iommu_{,un}map_page() -- __get_page_type() -- get_page_type()---
then, in this point, I try to deal with this iommu_{,un}map_page() error.
> > btw, there is another issue in the call path:
> > iommu_{,un}map_page() -- __get_page_type() -- get_page_type()---
> >
> >
> > I tried to return iommu_{,un}map_page() error code in
> > __get_page_type(), is it right?
>
> If the operation got fully rolled back - yes. Whether fully rolling back is feasible
> there though is - see the respective discussion - an open question.
>
For the open question, does it refer to as below:
"""
As said, we first need
to settle on an abstract model. Do we want IOMMU mapping
failures to be fatal to the domain (perhaps with the exception
of the hardware one)? I think we do, and for the hardware domain
we'd do things on a best effort basis (always erring on the side
of unmapping). Which would probably mean crashing the domain
could be centralized in iommu_{,un}map_page(). How much roll
back would then still be needed in callers of these functions
for the hardware domain's sake would need to be seen.
"""
I hope it is yes. I read all of your emails again and again, I found I did get the point until this Monday.
I am summarizing it and would send out in a new thread.
> >> > --- a/xen/drivers/passthrough/x86/iommu.c
> >> > +++ b/xen/drivers/passthrough/x86/iommu.c
> >> > @@ -104,7 +104,11 @@ int arch_iommu_populate_page_table(struct
> >> domain *d)
> >> > this_cpu(iommu_dont_flush_iotlb) = 0;
> >> >
> >> > if ( !rc )
> >> > - iommu_iotlb_flush_all(d);
> >> > + {
> >> > + rc = iommu_iotlb_flush_all(d);
> >> > + if ( rc )
> >> > + iommu_teardown(d);
> >> > + }
> >> > else if ( rc != -ERESTART )
> >> > iommu_teardown(d);
> >>
> >> Why can't you just use the existing call to iommu_teardown(), by
> >> simply
> > deleting
> >> the "else"?
> >>
> >
> > Just check it, could I modify it as below:
> > --- a/xen/drivers/passthrough/x86/iommu.c
> > +++ b/xen/drivers/passthrough/x86/iommu.c
> > @@ -105,7 +105,8 @@ int arch_iommu_populate_page_table(struct domain
> > *d)
> >
> > if ( !rc )
> > iommu_iotlb_flush_all(d);
> > - else if ( rc != -ERESTART )
> > +
> > + if ( rc != -ERESTART )
> > iommu_teardown(d);
>
> Clearly not - not only are you losing the return value of
> iommu_iotlb_flush_all() now, you would then also call
> iommu_teardown() in the "success" case. My comment was related to code
> structure, yet you seem to have taken it literally.
>
Then, what about this one:
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -104,8 +104,9 @@ int arch_iommu_populate_page_table(struct domain *d)
this_cpu(iommu_dont_flush_iotlb) = 0;
if ( !rc )
- iommu_iotlb_flush_all(d);
- else if ( rc != -ERESTART )
+ rc = iommu_iotlb_flush_all(d);
+
+ if ( !rc && rc != -ERESTART )
iommu_teardown(d);
IMO, my original modification is correct and redundant with 2 'iommu_teardown()'..
If this is still the correct one, could you help me send out the correct one?
Quan
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next prev parent reply other threads:[~2016-03-30 2:28 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-17 6:54 [PATCH 0/2] Check VT-d Device-TLB flush error Quan Xu
2016-03-17 6:54 ` [PATCH 1/2] IOMMU/MMU: Adjust top level functions for " Quan Xu
2016-03-17 7:32 ` Tian, Kevin
2016-03-17 7:58 ` Jan Beulich
2016-03-17 8:00 ` Tian, Kevin
2016-03-17 12:30 ` George Dunlap
2016-03-17 12:33 ` George Dunlap
2016-03-18 3:19 ` Xu, Quan
2016-03-18 8:09 ` Jan Beulich
2016-03-24 6:45 ` Xu, Quan
2016-03-18 7:54 ` Xu, Quan
2016-03-18 8:19 ` Jan Beulich
2016-03-18 9:09 ` Xu, Quan
2016-03-18 9:29 ` Jan Beulich
2016-03-18 9:38 ` Dario Faggioli
2016-03-18 9:48 ` Jan Beulich
2016-03-21 6:18 ` Tian, Kevin
2016-03-21 12:22 ` Jan Beulich
2016-03-24 9:02 ` Xu, Quan
2016-03-24 9:58 ` Jan Beulich
2016-03-24 14:12 ` Xu, Quan
2016-03-24 14:37 ` Jan Beulich
2016-03-17 17:14 ` Jan Beulich
2016-03-28 3:33 ` Xu, Quan
2016-03-29 7:20 ` Jan Beulich
2016-03-30 2:28 ` Xu, Quan [this message]
2016-03-30 2:35 ` Xu, Quan
2016-03-30 8:05 ` Jan Beulich
2016-03-17 6:54 ` [PATCH 2/2] IOMMU/MMU: Adjust low " Quan Xu
2016-03-17 7:37 ` Tian, Kevin
2016-03-18 2:30 ` Xu, Quan
2016-03-18 8:06 ` Jan Beulich
2016-03-21 5:01 ` Tian, Kevin
2016-03-17 15:31 ` George Dunlap
2016-03-18 6:57 ` Xu, Quan
2016-03-18 10:20 ` Jan Beulich
2016-03-25 9:27 ` Xu, Quan
2016-03-29 7:36 ` Jan Beulich
2016-04-11 3:09 ` Xu, Quan
2016-04-11 3:27 ` Xu, Quan
2016-04-11 16:34 ` Jan Beulich
2016-04-12 1:09 ` Xu, Quan
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