linux-kernel - Re: [PATCH] kvm: optimize ISR lookups

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:	Wed, 23 May 2012 18:10:09 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: optimize ISR lookups

On 05/22/2012 08:26 PM, Thomas Gleixner wrote:
> On Tue, 22 May 2012, Avi Kivity wrote:
>> On 05/22/2012 12:04 AM, Thomas Gleixner wrote:
>> > The only justification for having the same layout as the actual
>> > hardware is when you are going to map the memory into the guest space,
>> > which is not the case here.
>>
>> The APIC page is in fact mapped  to the hardware (not the guest, but vmx
>> microcode does access it).  Only one register, the TPR, is ever used. 
>> It's possible to re-layout the data structure so that the TPR stays in
>> the same place while everything else becomes contiguous, but we'll have
>> to do it again if the hardware starts mapping more registers.
> 
> I would avoid that by having a compressed version which reflects the
> SW state and the mapped one which allows the vmx microcode to fiddle
> with the TPR. If you need more registers in the HW page then you don't
> have to worry about the layout and just have a proper accessor for
> that.

That works, but replaces one problem with another: now we have two
sources for the same data, and need to juggle between them depending on
register number (either synchronizing in both directions, or special
casing); so you're simplifying one thing at the expense of the other.
If the microcode starts accessing more registers, then having two
layouts becomes even uglier.

-- 
error compiling committee.c: too many arguments to function
--
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/