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Re: [Xen-devel] Grant table corruption with HVM guest

To: "Justin T. Gibbs" <gibbs@xxxxxxxxxxx>
Subject: Re: [Xen-devel] Grant table corruption with HVM guest
From: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Sun, 14 Mar 2010 21:15:53 +0200
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On Sun, Mar 14, 2010 at 01:10:38PM -0600, Justin T. Gibbs wrote:
> I'm experiencing total grant table corruption on a system and I'm
> hoping my symptoms will ring a bell with a member of the Xen developer
> community.  The setup is Xen 4.0.0-RC2 (OpenSUSE 11.2 package) on
> a Nehalem system.

You should definitely upgrade to -rc6 or newer, since rc6 fixes
dom0 memory corruption bug!

I'm not sure if it's the same bug you're seeing..

-- Pasi

>  The sole guest instance is 64bit FreeBSD running
> in HVM mode, a single vcpu, and a PCI passed-through LSI Logic 1068e
> SAS controller.  FreeBSD is running netfront and blockfront PV
> drivers.  After a few hours of operation, FreeBSD's entire grant
> table (3 pages) is spammed with the pattern 0x5a5a5a5a.  This problem
> has been replicated on multiple machines.
> The first assumption was a bug in the FreeBSD PV drivers or other Xen
> support.  To rule this out, we modified FreeBSD's grant table functions
> to unmap the grant table from the kernel virtual address space between
> operations.  This was on a single vcpu setup, but to rule out corruption
> by interrupt handlers, interrupts were also disabled while the mapping was
> valid during grant table updates.  The corruption still occurs without the
> FreeBSD kernel faulting on unmapped pages.  I believe this leaves a VT-D
> HW problem or a bug in the hypervisor as the remaining possibilities.
> I'm working now to further isolate the error by changing our test load
> so I can remove VT-D from the configuration.
> Are there any Xen or QEMU components that use a 0x5a5a5a5a initialization
> pattern?  Are there any tools in the hypervisor I can use to trap rogue
> access to guest grant table pages?
> Thanks,
> Justin
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