From: Marcelo Tosatti <mtosatti@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>, kvm@vger.kernel.org
Subject: Re: cr3 OOS optimisation breaks 32-bit GNU/kFreeBSD guest
Date: Mon, 23 Feb 2009 12:06:38 -0300 [thread overview]
Message-ID: <20090223150638.GA5798@amt.cnet> (raw)
In-Reply-To: <49A2B9D9.3030103@redhat.com>
On Mon, Feb 23, 2009 at 04:59:37PM +0200, Avi Kivity wrote:
> Marcelo Tosatti wrote:
>>> Thanks for your fast answer and for your help for debugging.
>>>
>>
>> If you confirm that FreeBSD is indeed relying on cr3 to sync global
>> pages, it might be better to disable the optimization. Lets hope that is
>> not the case.
>>
>
> cr3 writes explicitly do not flush global pages; otherwise what would be
> the point of global pages at all?
From the Intel TLB doc:
The processor is always free to invalidate additional entries in the TLBs
and paging-structure caches. The following are some examples:
• MOV to CR3 may invalidate TLB entries for global pages.
The reasoning was if an optimization breaks an important guest which
contains a bug that happens to not trigger on real HW due to positioning
of the stars, it is reasonable to disable that optimization.
> In other words, the only difference between global and non-global pages
> is visible via cr3 writes.
next prev parent reply other threads:[~2009-02-23 15:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-23 0:33 cr3 OOS optimisation breaks 32-bit GNU/kFreeBSD guest Aurelien Jarno
2009-02-23 1:47 ` Marcelo Tosatti
2009-02-23 14:01 ` Aurelien Jarno
2009-02-23 14:52 ` Marcelo Tosatti
2009-02-23 14:59 ` Avi Kivity
2009-02-23 15:06 ` Marcelo Tosatti [this message]
2009-02-23 15:16 ` Avi Kivity
2009-03-20 23:14 ` Marcelo Tosatti
2009-03-21 8:51 ` Aurelien Jarno
2009-03-22 9:35 ` Avi Kivity
2009-03-23 17:27 ` Marcelo Tosatti
2009-03-24 9:47 ` Avi Kivity
2009-03-24 11:49 ` Marcelo Tosatti
2009-04-03 21:45 ` Marcelo Tosatti
2009-04-04 10:37 ` Avi Kivity
2009-04-04 17:01 ` Marcelo Tosatti
2009-04-05 8:41 ` Avi Kivity
2009-04-05 11:29 ` Marcelo Tosatti
2009-04-05 11:41 ` Avi Kivity
2009-04-04 23:23 ` Aurelien Jarno
2009-03-24 10:39 ` Aurelien Jarno
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