[Xen-users] Xen and Intel Debug Registers

["Matt Evenson" <mevenson@xxxxxxxxxx>]

Hi All,

Has anyone had issues with using CPU Debug Registers inside a VM
running under Xen?

I am getting inconsistent results when attempting to use the Intel
Debug Registers (DR0-DR7) in a Debian VM running inside a Xen 3.0.3
install.  I have found that after setting a breakpoint address
register (DR0-DR3) and correctly setting the debug control register
(DR7) two problems sometimes occur:

1. The breakpoint address register is randomly reset to 0
2. The control register is randomly reset to 0 (or 0x00000400)

This does not always happen, but often enough to be annoying.

If I run the exact same code on a domain 0 (non-virtualized) debian
install, the breakpoint and control register values function as
desired, every time.

I would love to hear if anyone else had had success or failure when
attempting to use Debug Registers inside a Xen VM.

Thanks,
Matt

p.s.  I'm running my Xen install on a dual-core intel cpu

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