On 08/03/2011 15:56, "Paul Durrant" <Paul.Durrant@xxxxxxxxxx> wrote:
> I still think this patch should stand. The locking around transitive grants is
> just borked and if someone actually does implement the rcu locks in future
> they will get a nasty surprise.
It will stand, in xen-unstable.
K.
> Paul
>
>> -----Original Message-----
>> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
>> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
>> Sent: 08 March 2011 15:39
>> To: George Dunlap; xen-devel@xxxxxxxxxxxxxxxxxxx
>> Subject: Re: [Xen-devel] [PATCH] Fix rcu domain locking for
>> transitive grants
>>
>> On 08/03/2011 15:11, "George Dunlap" <George.Dunlap@xxxxxxxxxxxxx>
>> wrote:
>>
>>> This should be backported to the 4.1 branch; it causes a
>> hypervisor
>>> BUG() if guests are using netchannel2 transtiive grants to talk to
>>> each other when debug mode is on.
>>
>> I stubbed out the preemption checking stuff in 4.1 branch (it's not
>> really needed since there are no users of waitqueues in 4.1), so
>> this patch is not required. And that's fortunate, since it's quite
>> non-trivial.
>>
>> -- Keir
>>
>>> -George
>>>
>>> On Tue, Mar 8, 2011 at 3:02 PM, George Dunlap
>>> <george.dunlap@xxxxxxxxxxxxx> wrote:
>>>> When acquiring a transitive grant for copy then the owning domain
>>>> needs to be locked down as well as the granting domain. This was
>>>> being done, but the unlocking was not. The acquire code now
>> stores
>>>> the struct domain * of the owning domain (rather than the domid)
>> in
>>>> the active entry in the granting domain. The release code then
>> does the unlock on the owning domain.
>>>> Note that I believe I also fixed a bug where, for non-transitive
>>>> grants the active entry contained a reference to the acquiring
>> domain
>>>> rather than the granting domain. From my reading of the code this
>>>> would stop the release code for transitive grants from
>> terminating
>>>> its recursion correctly.
>>>>
>>>> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
>>>> CC: Steven Smith <steven.smith@xxxxxxxxxx>
>>>>
>>>> diff -r f071d8e9f744 -r 14211e98efac xen/common/grant_table.c
>>>> --- a/xen/common/grant_table.c Tue Mar 08 10:23:52 2011 +0000
>>>> +++ b/xen/common/grant_table.c Tue Mar 08 14:39:03 2011 +0000
>>>> @@ -1626,11 +1626,10 @@
>>>> struct active_grant_entry *act;
>>>> unsigned long r_frame;
>>>> uint16_t *status;
>>>> - domid_t trans_domid;
>>>> grant_ref_t trans_gref;
>>>> int released_read;
>>>> int released_write;
>>>> - struct domain *trans_dom;
>>>> + struct domain *td;
>>>>
>>>> released_read = 0;
>>>> released_write = 0;
>>>> @@ -1644,15 +1643,13 @@
>>>> if (rd->grant_table->gt_version == 1)
>>>> {
>>>> status = &sha->flags;
>>>> - trans_domid = rd->domain_id;
>>>> - /* Shut the compiler up. This'll never be used, because
>>>> - trans_domid == rd->domain_id, but gcc doesn't know
>> that.
>>>> */
>>>> - trans_gref = 0x1234567;
>>>> + td = rd;
>>>> + trans_gref = gref;
>>>> }
>>>> else
>>>> {
>>>> status = &status_entry(rd->grant_table, gref);
>>>> - trans_domid = act->trans_dom;
>>>> + td = act->trans_domain;
>>>> trans_gref = act->trans_gref;
>>>> }
>>>>
>>>> @@ -1680,21 +1677,16 @@
>>>>
>>>> spin_unlock(&rd->grant_table->lock);
>>>>
>>>> - if ( trans_domid != rd->domain_id )
>>>> + if ( td != rd )
>>>> {
>>>> - if ( released_write || released_read )
>>>> - {
>>>> - trans_dom = rcu_lock_domain_by_id(trans_domid);
>>>> - if ( trans_dom != NULL )
>>>> - {
>>>> - /* Recursive calls, but they're tail calls, so
>> it's
>>>> - okay. */
>>>> - if ( released_write )
>>>> - __release_grant_for_copy(trans_dom,
>> trans_gref,
>>>> 0);
>>>> - else if ( released_read )
>>>> - __release_grant_for_copy(trans_dom,
>> trans_gref,
>>>> 1);
>>>> - }
>>>> - }
>>>> + /* Recursive calls, but they're tail calls, so it's
>>>> + okay. */
>>>> + if ( released_write )
>>>> + __release_grant_for_copy(td, trans_gref, 0);
>>>> + else if ( released_read )
>>>> + __release_grant_for_copy(td, trans_gref, 1);
>>>> +
>>>> + rcu_unlock_domain(td);
>>>> }
>>>> }
>>>>
>>>> @@ -1731,7 +1723,7 @@
>>>> uint32_t old_pin;
>>>> domid_t trans_domid;
>>>> grant_ref_t trans_gref;
>>>> - struct domain *rrd;
>>>> + struct domain *td;
>>>> unsigned long gfn;
>>>> unsigned long grant_frame;
>>>> unsigned trans_page_off;
>>>> @@ -1785,8 +1777,8 @@
>>>> status) ) != GNTST_okay )
>>>> goto unlock_out;
>>>>
>>>> - trans_domid = ld->domain_id;
>>>> - trans_gref = 0;
>>>> + td = rd;
>>>> + trans_gref = gref;
>>>> if ( sha2 && (shah->flags & GTF_type_mask) ==
>> GTF_transitive
>>>> )
>>>> {
>>>> if ( !allow_transitive )
>>>> @@ -1808,14 +1800,15 @@
>>>> that you don't need to go out of your way to avoid
>> it
>>>> in the guest. */
>>>>
>>>> - rrd = rcu_lock_domain_by_id(trans_domid);
>>>> - if ( rrd == NULL )
>>>> + /* We need to leave the rrd locked during the grant
>> copy
>>>> + */
>>>> + td = rcu_lock_domain_by_id(trans_domid);
>>>> + if ( td == NULL )
>>>> PIN_FAIL(unlock_out, GNTST_general_error,
>>>> "transitive grant referenced bad domain
>>>> %d\n",
>>>> trans_domid);
>>>> spin_unlock(&rd->grant_table->lock);
>>>>
>>>> - rc = __acquire_grant_for_copy(rrd, trans_gref, rd,
>>>> + rc = __acquire_grant_for_copy(td, trans_gref, rd,
>>>> readonly, &grant_frame,
>>>> &trans_page_off,
>>>> &trans_length,
>>>> 0, &ignore); @@ -1823,6
>>>> +1816,7 @@
>>>> spin_lock(&rd->grant_table->lock);
>>>> if ( rc != GNTST_okay ) {
>>>> __fixup_status_for_pin(act, status);
>>>> + rcu_unlock_domain(td);
>>>> spin_unlock(&rd->grant_table->lock);
>>>> return rc;
>>>> }
>>>> @@ -1834,6 +1828,7 @@
>>>> if ( act->pin != old_pin )
>>>> {
>>>> __fixup_status_for_pin(act, status);
>>>> + rcu_unlock_domain(td);
>>>> spin_unlock(&rd->grant_table->lock);
>>>> return __acquire_grant_for_copy(rd, gref, ld,
>>>> readonly,
>>>> frame, page_off,
>>>> length, @@ -1845,7 +1840,7 @@
>>>> sub-page, but we always treat it as one because
>> that
>>>> blocks mappings of transitive grants. */
>>>> is_sub_page = 1;
>>>> - *owning_domain = rrd;
>>>> + *owning_domain = td;
>>>> act->gfn = -1ul;
>>>> }
>>>> else if ( sha1 )
>>>> @@ -1891,7 +1886,7 @@
>>>> act->is_sub_page = is_sub_page;
>>>> act->start = trans_page_off;
>>>> act->length = trans_length;
>>>> - act->trans_dom = trans_domid;
>>>> + act->trans_domain = td;
>>>> act->trans_gref = trans_gref;
>>>> act->frame = grant_frame;
>>>> }
>>>> diff -r f071d8e9f744 -r 14211e98efac
>> xen/include/xen/grant_table.h
>>>> --- a/xen/include/xen/grant_table.h Tue Mar 08 10:23:52 2011
>>>> +0000
>>>> +++ b/xen/include/xen/grant_table.h Tue Mar 08 14:39:03 2011
>>>> +++ +0000
>>>> @@ -32,7 +32,7 @@
>>>> struct active_grant_entry {
>>>> u32 pin; /* Reference count
>> information.
>>>> */
>>>> domid_t domid; /* Domain being granted
>> access.
>>>> */
>>>> - domid_t trans_dom;
>>>> + struct domain *trans_domain;
>>>> uint32_t trans_gref;
>>>> unsigned long frame; /* Frame being
>> granted.
>>>> */
>>>> unsigned long gfn; /* Guest's idea of the frame being
>> granted.
>>>> */
>>>>
>>>> _______________________________________________
>>>> Xen-devel mailing list
>>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>>> http://lists.xensource.com/xen-devel
>>>>
>>>
>>> _______________________________________________
>>> Xen-devel mailing list
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>>> http://lists.xensource.com/xen-devel
>>
>>
>>
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