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Re: [Xen-devel] General protection fault in netback

On Wed, Feb 22, 2012 at 03:17:24PM +0300, Anton Samsonov wrote:
> 2012/2/21 Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>:
> AS>> With custom-built kernel, I didn't yet see any GPF, but screen garbling
> AS>> happens almost every time when a DomU is starting or stopping:
> AS>> the whole graphical is painted with either black or not-so-random 
> garbage.
> KRW> So... I am curious, what graphic card do you have and do you get any of
> KRW> these Red Hat BZs? ÂRH BZ# 742032, 787403, and 745574?
> KRW> There is a bug in 3.2 when using radeon or nouveau for a lengthy time
> KRW> that ends up "corrupting" memory. The workaround is 'nopat' kernel arg.
> My idea is that my custom-built kernel can't be considered a trusted
> proving ground,
> as it is of very low quality. Video issue is just the most obvious
> example. Another
> indisputable example is how the Dom0 reboots: instead of simple CPU restart,
> the whole system goes into soft-off for several seconds, then wakes back.
> When I boot this kernel in bare-metal mode (without Xen VMM), none of those
> happens: GUI is accelerated (at least in 2D; I don't use OpenGL desktop),
> screen is not garbled at login and logout dialogs, system reboots quickly.
> Anyway, I tried your solution with "nopat". It didn't worked: with 4
> DomUs running
> for a minute and then shut down in reverse order (4th, 3rd, 2nd, 1st),
> the screen
> went black right between the 3rd VM was completely shut and 2nd VM was
> requested to shut. There was no "lengthy time" of Dom0 running, my video 
> adapter
> is neither nVidia nor ATi, but an integrated Intel HD Graphics 2000
> using i915 driver,
> and I see no similarities to the Red Hat bugs mentioned by you.
> KRW> Can you include more details on your machine?
> My guess is that it is not just my hardware that causes GPF, but either
> a bug in netback module, or a compiler issue for specific combination of Xen
> (and/or particularly netback) together with openSUSE build technology.
> As an example of the latter, look again at the Novell BZ #727081 mentioned
> in the original post â the comment #30 says: "The compiler apparently makes 
> use
> of the 128-byte area called 'red zone' in the ABI, and this is incompatible
> with xc_cpuid_x86.c:cpuid() using pushes and pops around the cpuid 
> instruction".
> The consequence is that, on some machines, libxenguest segfaults when you
> try to start a DomU. With Core i7-920 there is no problem, but with Core 
> i5-2300
> I faced that issue, and wonder whether the same incompatibility can take place
> in netback module. I though the traceback gives some hints on where to debug.
> My specs are:
> MB: Asus P8H67-M (Intel H67 chipset)
> CPU: Intel Core i5 model 2300 (Turbo mode disabled)
> RAM: 12GB DDR3-1333 non-ECC (recently checked by MemTest86+ 4.20)

Do you have CONFIG_DMAR enabled in your config?

> Video: Intel HD Graphics 2000 (integrated into CPU)
> Network: dedicated soft-bridge for most DomUs,
>  + bridged Realtek RTL8111E for gateway DomU (not with CARP)

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