tree b73e2b470a959e60fb5332737c1fca04bb629ba7
parent ff54250a0ebab7f90a5f848a0ba63f999830c872
author Matias Zabaljauregui <zabaljauregui@gmail.com> 1239224319 -0300
committer Rusty Russell <rusty@rustcorp.com.au> 1240148640 +0930

lguest: fix crash on vmlinux images

Typical message: 'lguest: unhandled trap 6 at 0x418726 (0x0)'

vmlinux guests were broken by 4cd8b5e2a159f18a1507f1187b44a1acbfa6341b
'lguest: use KVM hypercalls', which rewrites guest text from kvm hypercalls
to trap 31.

The Launcher mmaps the kernel image.  The Guest executes and
immediately faults in the first text page (read-only).  Then it hits a
hypercall, and we rewrite that hypercall, causing a copy-on-write.
But the Guest pagetables still refer to the old page: we fault again,
but as Host we see the hypercall already rewritten, and pass the fault
back to the Guest.  The Guest hasn't set up an IDT yet, so we kill it.

This doesn't happen with bzImages: they unpack themselves and so the
text pages are already read-write.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Tested-by: Patrick McHardy <kaber@trash.net>