linux-kernel - Re: [GIT PULL] Xen APIC hooks (with io_apic

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, 25 May 2009 07:19:54 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [GIT PULL] Xen APIC hooks (with io_apic_ops)


* Avi Kivity <avi@...hat.com> wrote:

> Ingo Molnar wrote:
>> * Avi Kivity <avi@...hat.com> wrote:
>>
>>   
>>> Ingo Molnar wrote:
>>>     
>>>>> We do something similar for Windows (by patching it) very   
>>>>> successfully; Windows likes to touch the APIC TPR ~ 100,000 times 
>>>>>  per second, usually without triggering an interrupt.  We hijack  
>>>>> these writes, do the checks in guest context, and only exit if 
>>>>> the  TPR write would trigger an interrupt.
>>>>>             
>>>> I suspect you aware of that this is about the io-apic not the local 
>>>>  APIC. The local apic methods are already driver-ized - and they 
>>>> sit  closer to the CPU so they matter more to performance.
>>>>         
>>> Yeah, I gave this as an example.  It's very different -- io-apic vs.  
>>> local apic, paravirtualization vs. patching the guest behind its 
>>> back, Linux vs. Windows.
>>>
>>> Of course if we hook the io-apic EOI we'll want to hook the local  
>>> apic EOI as well.
>>>     
>>
>> Yeah. Eventually anything that matters to performance will be 
>> accelerated by hardware (and properly virtualized), which in turn 
>> will be faster than any hypercall based approach, right?
>
> Right.  That's already happened to the TPR (Intel processors 
> accelerate that 4-bit registers but ignore everything else in the 
> local apic).  As another example, we have mmu paravirtualization 
> in kvm, but automatically disable it when the hardware does nested 
> paging.  The problem is that hardware support has a long pipeline, 
> and even when support does appear, there's a massive installed 
> base to care about.

Yeah. Btw., i also think that in-kernel IO-APIC and APIC emulation 
could have uses elsewhere as well - such as in testing. Currently 
you actually have to own a big box to be able to test certain 
hardware limits. This has a negative effect on test coverage and a 
subsequent negative effect on kernel quality. If KVM provided clean 
code to emulate certain hw environments we could check out limits 
(and our bugs) far more effectively.

	Ingo
--
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/