linux-kernel - Re: [Qemu-devel] SCSI bus failures with qemu-arm in kernel 3.8+

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]

Message-ID: <520D53CA.6040807@roeck-us.net>
Date:	Thu, 15 Aug 2013 15:18:50 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Peter Maydell <peter.maydell@...aro.org>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	QEMU Developers <qemu-devel@...gnu.org>,
	Arnd Bergmann <arnd.bergmann@...aro.org>
Subject: Re: [Qemu-devel] SCSI bus failures with qemu-arm in kernel 3.8+

On 08/15/2013 02:49 PM, Peter Maydell wrote:
> On 15 August 2013 21:50, Guenter Roeck <linux@...ck-us.net> wrote:
>> On Thu, Aug 15, 2013 at 07:05:22PM +0100, Peter Maydell wrote:
>>> It needs to go in the same patch, because a kernel with the fixed
>>> irq remapping must also tell QEMU it is fixed; if you split the
>>> two then at the point between the two patches the kernel is
>>> broken for bisection purposes.
>>>
>> Thinking about it - is that really true ? My image with the
>> patch applied works just fine under qemu 1.5.2, and unless
>> I am missing something it won't work with qemu 1.4 anyway.
>> So what exactly is broken ?
>
> You're OK unless the kernel happens to pick the same interrupt
> number to write to PCI_INTERRUPT_LINE as one of the previous
> broken kernel versions did (in which case QEMU will incorrectly
> assume you're a broken kernel). This can't happen with the way
> the kernel is currently picking interrupt numbers (ie with a
> straightforward relationship between h/w irqs and values written),
> but as I understand from Arnd there is a plan to move to a
> different approach ("sparse irqs") at which point this won't hold:
> http://lists.gnu.org/archive/html/qemu-devel/2013-03/msg04579.html
> So it's better for the kernel to make sure it gets the
> behaviour it wants rather than getting unpleasant surprises
> later.
>

But doesn't that mean that there is _currently_ no problem ? If so,
we can introduce the additional code when the problem really shows up.
Being Preemptive is good, but if it is not really needed today
I would rather have today's problems resolved and bother about tomorrow's
when they show up.

Guenter

--
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/