Gabe Black wrote:
Hi. I'm a developer on the M5 simulator (m5sim.org) working on a CPU
model which uses kvm as its execution engine.
Neat stuff. You're using kvm to run non-x86 code on x86?
I ran into a kernel "BUG"
where a NULL pointer is being dereferenced in gfn_to_rmap.
What's happening on the kernel side is that gfn_to_rmap is calling
gfn_to_memslot. That function looks for the gfn in the memory slots,
fails to find it, and returns a NULL pointer. gfn_to_rmap then tries to
dereference it, and the kernel kills itself. I believe the original
source of the call to gfn_to_memslot was mmu_alloc_roots (in 2.6.28.9,
it may have moved) which tries to get the page pointed to by CR3 using
kvm_mmu_get_page. That part may not be correct, so here's the log output
from the kernel.
This was fixed by 89da4ff17 ("KVM: x86: check for cr3 validity in
mmu_alloc_roots"). Did the code base you were testing contain that?7
The second problem was the fact that CR3 didn't point to any memory even
though it had a valid value (0x7000). This was because our code relied
on kvm_create to set up physical memory, and while it takes parameters
for it and passes them around, it never actually seems to do anything
with them. This also seems to be the case in your most recent code.
You should set up the memory independently using the memory slot APIs,
then load CR3. kvm_create() has bitrotted a bit.
I am a full time employee of VMware, and while I work on M5 on my own
time, that places certain limits on what I can do to help fix these
bugs. While I probably can't implement anything, I should be able to
provide more information about what we're doing with M5 or about the
crash if that would help.
I appreciate the reports. Please test latest kvm.git and let us know if
the problems persist.
It would also be interesting to hear how you use kvm.
--
error compiling committee.c: too many arguments to function
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