linux-kernel - Re: [PATCH] KVM: IOAPIC: only access APIC registers one dword at a time

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Date:	Fri, 02 Jul 2010 15:38:02 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Jin Dongming <jin.dongming@...css.fujitsu.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: IOAPIC: only access APIC registers one dword at
 a time



Jin Dongming wrote:

>>  
>>  	switch (len) {
>> -	case 8:
>> -		*(u64 *) val = result;
>> -		break;
>> -	case 1:
>> -	case 2:
>>  	case 4:
>> -		memcpy(val, (char *)&result, len);
> 
> Here the parameter len is not used for reading data from ioapic register, before switch case
> the value of ioapic register has been read by ioapic_read_indirect().
> 

Yeah, it's right, but it's rarely operation that guest using incorrect width to access
the registers, so i don't think it's worthy to move the width judgment before the real
registers read.

> 
>> +		*(u32 *) val = result;
>>  		break;
>> +
>>  	default:
>>  		printk(KERN_WARNING "ioapic: wrong length %d\n", len);
> 
> And I think here is not good to print warning message. Maybe it is better to do
> such kind of checking at the first of this function before ioapic_read_indirect().
> 

ditto

Thanks for your review, Jin!
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