linux-kernel - Re: [PATCH v2 03/16] KVM: MMU: properly assert spte on rmap walking path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 16 Apr 2012 11:26:19 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 03/16] KVM: MMU: properly assert spte on rmap walking
 path

On 04/14/2012 10:15 AM, Takuya Yoshikawa wrote:

> On Fri, 13 Apr 2012 18:10:45 +0800
> Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:
> 
>>  static u64 *rmap_get_next(struct rmap_iterator *iter)
>>  {
>> +	u64 *sptep = NULL;
>> +
>>  	if (iter->desc) {
>>  		if (iter->pos < PTE_LIST_EXT - 1) {
>> -			u64 *sptep;
>> -
>>  			++iter->pos;
>>  			sptep = iter->desc->sptes[iter->pos];
>>  			if (sptep)
>> -				return sptep;
>> +				goto exit;
>>  		}
>>
>>  		iter->desc = iter->desc->more;
>> @@ -1028,11 +1036,14 @@ static u64 *rmap_get_next(struct rmap_iterator *iter)
>>  		if (iter->desc) {
>>  			iter->pos = 0;
>>  			/* desc->sptes[0] cannot be NULL */
>> -			return iter->desc->sptes[iter->pos];
>> +			sptep = iter->desc->sptes[iter->pos];
>> +			goto exit;
>>  		}
>>  	}
>>
>> -	return NULL;
>> +exit:
>> +	WARN_ON(sptep && !is_shadow_present_pte(*sptep));
>> +	return sptep;
>>  }
> 
> This will, probably, again force rmap_get_next function-call even with EPT/NPT:
> CPU cannot skip it by branch prediction.
> 

No, EPT/NPT also needs it.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/