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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Julien Grall <julien.grall@arm.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH for-4.10] passthrough/vtd: Don't DMA to the stack in queue_invalidate_wait()
Date: Thu, 19 Oct 2017 14:31:33 +0100	[thread overview]
Message-ID: <6d299384-aa28-1bea-eb9e-f1a4c974d128@citrix.com> (raw)
In-Reply-To: <59E8C3DA0200007800188265@prv-mh.provo.novell.com>

On 19/10/17 14:25, Jan Beulich wrote:
>>>> On 19.10.17 at 14:54, <andrew.cooper3@citrix.com> wrote:
>> On 19/10/17 13:11, Jan Beulich wrote:
>>>>>> On 19.10.17 at 13:26, <andrew.cooper3@citrix.com> wrote:
>>>> --- a/xen/drivers/passthrough/vtd/qinval.c
>>>> +++ b/xen/drivers/passthrough/vtd/qinval.c
>>>> @@ -147,7 +147,8 @@ static int __must_check queue_invalidate_wait(struct iommu *iommu,
>>>>                                                u8 iflag, u8 sw, u8 fn,
>>>>                                                bool_t flush_dev_iotlb)
>>>>  {
>>>> -    volatile u32 poll_slot = QINVAL_STAT_INIT;
>>> You've lost the initializer.
>> Deliberately so.
> I don't understand: By never writing QINVAL_STAT_INIT, how can
> multiple waits work? Afaict you'll find the variable set to
> QINVAL_STAT_DONE the 2nd time you come here, and hence you
> won't wait at all.

Oh yes - you are quite correct.

My test box, which does end up doing frequent queued invalidations,
doesn't appear to suffer any bad side effects from this
quite-clearly-wrong code.

~Andrew

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  reply	other threads:[~2017-10-19 13:31 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-19 11:26 [PATCH for-4.10] passthrough/vtd: Don't DMA to the stack in queue_invalidate_wait() Andrew Cooper
2017-10-19 12:11 ` Jan Beulich
2017-10-19 12:54   ` Andrew Cooper
2017-10-19 13:25     ` Jan Beulich
2017-10-19 13:31       ` Andrew Cooper [this message]
2017-10-19 16:22 ` [PATCH for-4.10 v2] " Andrew Cooper
2017-10-20  7:12   ` Jan Beulich
2017-10-20 17:55     ` Andrew Cooper
2017-10-23  7:05       ` Tian, Kevin
     [not found]       ` <AADFC41AFE54684AB9EE6CBC0274A5D190E3101C@SHSMSX101.ccr.corp.intel.com>
2017-10-23  7:06         ` Tian, Kevin
2017-10-23  7:18       ` Jan Beulich
2017-10-23  8:06         ` Andrew Cooper

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