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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Lin Ming <mlin@ss.pku.edu.cn>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall
Date: Fri, 20 Apr 2012 13:53:23 +0100	[thread overview]
Message-ID: <4F915C43.4020207@citrix.com> (raw)
In-Reply-To: <1334925508.28331.63.camel@zakaz.uk.xensource.com>

On 20/04/12 13:38, Ian Campbell wrote:
> On Fri, 2012-04-20 at 12:13 +0100, Lin Ming wrote:
>> On Fri, 2012-04-20 at 10:58 +0100, Andrew Cooper wrote:
>>> On 20/04/12 10:25, Lin Ming wrote:
>>>> Implements xen_io_apic_read with hypercall, so it returns proper IO-APIC
>>>> information instead of fabricated one.
>>>>
>>>> Signed-off-by: Lin Ming <mlin@ss.pku.edu.cn>
>>>> ---
>>>>  arch/x86/xen/apic.c |   16 +++++++++++-----
>>>>  1 files changed, 11 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c
>>>> index aee16ab..f1f392d 100644
>>>> --- a/arch/x86/xen/apic.c
>>>> +++ b/arch/x86/xen/apic.c
>>>> @@ -1,14 +1,20 @@
>>>>  #include <linux/init.h>
>>>>  #include <asm/x86_init.h>
>>>> +#include <asm/apic.h>
>>>> +#include <xen/interface/physdev.h>
>>>> +#include <asm/xen/hypercall.h>
>>>>  
>>>>  unsigned int xen_io_apic_read(unsigned apic, unsigned reg)
>>>>  {
>>>> -	if (reg == 0x1)
>>>> -		return 0x00170020;
>>>> -	else if (reg == 0x0)
>>>> -		return apic << 24;
>>>> +	struct physdev_apic apic_op;
>>>> +	int ret;
>>>>  
>>>> -	return 0xff;
>>>> +	apic_op.apic_physbase = mpc_ioapic_addr(apic);
>>>> +	apic_op.reg = reg;
>>>> +	ret = HYPERVISOR_physdev_op(PHYSDEVOP_apic_read, &apic_op);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +	return apic_op.value;
>>> Hypercall ret errors are negative, yet this function is unsigned.  Given
>>> that the previous function had no possible way to fail, perhaps on error
>>> you should fake up the values as before.
>> How about return -1 on error?
>> The calling function can check -1 for error. 
> Isn't -1 potentially (at least theoretically) a valid value to read from
> one of these registers?

Theoretically yes, but practically it would only be buggy hardware
returning -1.

>
> 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).  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.

>
>> unsigned int ret = apic_read(...);
>> if (ret == -1)
>> 	//handle error.
>>
>> Thanks,
>> Lin Ming
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xen.org
>> http://lists.xen.org/xen-devel
>

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


  parent reply	other threads:[~2012-04-20 12:53 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 [this message]
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             ` [Xen-devel] " Jan Beulich
2012-04-20 15:06             ` 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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