From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Yang Z Zhang <yang.z.zhang@intel.com>,
xen-devel <xen-devel@lists.xenproject.org>,
xiantao.zhang@intel.com
Subject: Re: [PATCH 1/4] VT-d/qinval: make local variable used for communication with IOMMU "volatile"
Date: Mon, 16 Jun 2014 13:55:31 +0100 [thread overview]
Message-ID: <539EE943.90702@citrix.com> (raw)
In-Reply-To: <539F038C020000780001AA34@mail.emea.novell.com>
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On 16/06/14 13:47, Jan Beulich wrote:
> Without that there is - afaict - nothing preventing the compiler from
> putting the variable into a register for the duration of the wait loop.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
I seem to remember Tim saying that behaviour like this is covered by
-fno-strict-aliasing
Either way, it is certainly correct for it to be marked as volatile.
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>
> --- a/xen/drivers/passthrough/vtd/qinval.c
> +++ b/xen/drivers/passthrough/vtd/qinval.c
> @@ -196,7 +196,7 @@ static int queue_invalidate_wait(struct
> u8 iflag, u8 sw, u8 fn)
> {
> s_time_t start_time;
> - u32 poll_slot = QINVAL_STAT_INIT;
> + volatile u32 poll_slot = QINVAL_STAT_INIT;
> int index = -1;
> int ret = -1;
> unsigned long flags;
>
>
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
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next prev parent reply other threads:[~2014-06-16 12:55 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-16 12:42 [PATCH 0/4] VT-d/qinval: miscellaneous adjustments Jan Beulich
2014-06-16 12:47 ` [PATCH 1/4] VT-d/qinval: make local variable used for communication with IOMMU "volatile" Jan Beulich
2014-06-16 12:55 ` Andrew Cooper [this message]
2014-06-16 13:03 ` Jan Beulich
2014-06-20 2:09 ` Zhang, Yang Z
2014-06-16 12:48 ` [PATCH 2/4] VT-d: drop redundant calls to invalidate_sync() Jan Beulich
2014-06-16 13:08 ` Andrew Cooper
2014-06-20 2:10 ` Zhang, Yang Z
2014-06-16 12:48 ` [PATCH 3/4] VT-d/qinval: clean up error handling Jan Beulich
2014-06-16 13:55 ` Andrew Cooper
2014-06-20 2:12 ` Zhang, Yang Z
2014-06-20 7:27 ` Jan Beulich
2014-06-20 11:30 ` Zhang, Yang Z
2014-06-16 12:49 ` [PATCH 4/4] VT-d/qinval: queue index is always unsigned Jan Beulich
2014-06-16 13:56 ` Andrew Cooper
2014-06-20 2:11 ` Zhang, Yang Z
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