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From: "Jan Beulich" <JBeulich@suse.com>
To: "Lin Ming" <mlin@ss.pku.edu.cn>
Cc: "Andrew Cooper" <Andrew.Cooper3@citrix.com>,
	"Ian Campbell" <Ian.Campbell@citrix.com>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall
Date: Fri, 20 Apr 2012 15:59:10 +0100	[thread overview]
Message-ID: <4F9195DE020000780007EEB1@nat28.tlf.novell.com> (raw)
In-Reply-To: <CAF1ivSaPshQf=BZ1gKLUq1yRF_MWeyjjVWkfv+E_jT+K5CFmAA@mail.gmail.com>

>>> On 20.04.12 at 16:50, Lin Ming <mlin@ss.pku.edu.cn> wrote:
> On Fri, Apr 20, 2012 at 9:12 PM, Ian Campbell <Ian.Campbell@citrix.com> wrote:
>> On Fri, 2012-04-20 at 13:53 +0100, Andrew Cooper wrote:
>>> >
>>> > Under what circumstances can these hypercalls fail? Would a BUG_ON be
>>> > appropriate/
>>>
>>> -EFAULT, -EPERM, anything xsm_apic() could return (which looks only to
>>> be -EPERM).
>>
>> So either the guest has called a hypercall which it is not permitted to
>> or it has called it with invalid parameters of one sort or another. Both
>> of these would be a code bug in the guest and therefore asserting that
>> no failure occurred is reasonable?
>>
>> What could the caller do with the error other than log it and collapse?
>>
>>> The call into Xen itself will return 0 as a value if an
>>> invalid physbase is passed in the hypercall.
>>
>>> So a BUG_ON() is not safe/sensible for domU.
>>
>> I think you have successfully argued that it is ;-)
> 
> BUG_ON is too severe. How about WARN_ON?
> 
> ret = hypercall(...)
> 
> if (ret) {
>    WARN_ON(1);
>    return -1;
> }

But if you go with this, please use the more modern

if (WARN_ON(ret))
	return -1;

Jan


  reply	other threads:[~2012-04-20 14:59 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-20  9:25 Lin Ming
2012-04-20  9:58 ` [Xen-devel] " Andrew Cooper
2012-04-20 11:13   ` Lin Ming
2012-04-20 12:38     ` Ian Campbell
2012-04-20 12:52       ` Jan Beulich
2012-04-20 12:53       ` Andrew Cooper
2012-04-20 13:12         ` Ian Campbell
2012-04-20 13:20           ` Andrew Cooper
2012-04-20 14:50           ` Lin Ming
2012-04-20 14:50             ` Lin Ming
2012-04-20 14:59             ` Jan Beulich [this message]
2012-04-20 15:06             ` [Xen-devel] " Ian Campbell
2012-04-20 15:39               ` Lin Ming
2012-04-20 16:43                 ` Konrad Rzeszutek Wilk
2012-04-20 16:41       ` Konrad Rzeszutek Wilk
2012-04-23  8:42         ` Lin Ming
2012-04-23 15:11           ` Konrad Rzeszutek Wilk
2012-04-24 14:43             ` Lin Ming
2012-04-24 16:23               ` Konrad Rzeszutek Wilk
2012-04-25 10:06                 ` Lin Ming
2012-04-26 15:33                   ` Konrad Rzeszutek Wilk
2012-04-26 15:33                     ` Konrad Rzeszutek Wilk

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