[Xen-devel] Re: [PATCH] Fix debug exception stack to enable gdb on xeno64

[Andi Kleen <ak@xxxxxxx>]

"Li, Xin B" <xin.b.li@xxxxxxxxx> writes:

> Native x86_64 linux uses paranoidentry for exceptions with ist != 0,
> while x86_64 xenlinux doesn't have special stacks for these exceptions.
> Actually we don't need paranoidentry for x86_64 xenlinux, and these
> exceptions except #DB should be handled in hypervisor.  With this patch,
> #DB is forwarded to guest, and let it use zeroentry should be OK.
> -Xin

Doesn't look correct to me. When you get an NMI or DB directly after 
a SYSCALL to Xen it'll execute on a random stack and likely break
if the guest runs with a broken stack at that time.

Also I can really recommend having IST stacks for double fault and stack
fault, otherwise everytime you break the stack you get a triple fault
which are nasty to debug. You guys with target probes might not
care that much, but others do.

-Andi

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