linux-kernel - Re: [PATCH 1/5] Add a global synchronization point for pvclock

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:	Fri, 23 Apr 2010 11:31:37 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Glauber Costa <glommer@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Peter Zijlstra <peterz@...radead.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

On 04/22/2010 11:34 PM, Avi Kivity wrote:
> On 04/23/2010 04:44 AM, Zachary Amsden wrote:
>>    Or apply this patch.
>> time-warp.patch
>>
>>
>> diff -rup a/time-warp-test.c b/time-warp-test.c
>> --- a/time-warp-test.c    2010-04-15 16:30:13.955981607 -1000
>> +++ b/time-warp-test.c    2010-04-15 16:35:37.777982377 -1000
>> @@ -91,7 +91,7 @@ static inline unsigned long long __rdtsc
>>   {
>>       DECLARE_ARGS(val, low, high);
>>
>> -    asm volatile("cpuid; rdtsc" : EAX_EDX_RET(val, low, high));
>> +    asm volatile("cpuid; rdtsc" : EAX_EDX_RET(val, low, high) :: 
>> "ebx", "ecx");
>>
>
> Plus, replace cpuid by lfence/mfence.  cpuid will trap.
>

Does lfence / mfence actually serialize?  I thought there was some great 
confusion about that not being the case on all AMD processors, and 
possibly not at all on Intel.

A trap, however is a great way to serialize.

I think, there is no serializing instruction which can be used from 
userspace which does not trap, at least, I don't know one off the top of 
my head.

Zach
--
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/