Mailing List Archive: traps and call back mechanism in XEN

Hello,

I am trying to figure out how the trap and callback mechanism works
between a guest OS and XEN. When a guest OS starts up, it uses the
HYPERVISOR_set_trap_table() to register a set of traps with XEN.
For example, it registers the trap that will handle a divide_error or
page_fault exception.

Now when XEN gets an exception, XEN executes the do_trap() function that
is found in xen/arch/x86/traps.c.
do_trap() retrieves the current domain's trap information that was registered
with HYPERVISOR_set_trap_table() and fills in a structure called
"guest_trap_bounce". From that point on, I don't quite follow how the guest OS
comes into play to handle the exception. Could someone please give me some
directions.

Thank You
Richard

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> Hello,
>
> I am trying to figure out how the trap and callback mechanism works
> between a guest OS and XEN. When a guest OS starts up, it uses the
> HYPERVISOR_set_trap_table() to register a set of traps with XEN.
> For example, it registers the trap that will handle a divide_error or
> page_fault exception.
>
> Now when XEN gets an exception, XEN executes the do_trap() function that
> is found in xen/arch/x86/traps.c.
> do_trap() retrieves the current domain's trap information that was registered
> with HYPERVISOR_set_trap_table() and fills in a structure called
> "guest_trap_bounce". From that point on, I don't quite follow how the guest OS
> comes into play to handle the exception. Could someone please give me some
> directions.

The guest_trap_counce is interpreted in arch/x86/x86_32/entry.S and
used to create a stack frame on the ring-1 (guest OS) stack.

-- Keir

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