Hi Everyone,
I've just pushed my kvm+x86 patches to github. The KVM patches are in
the 'kvm-x86' branch [1]. I have rebased them onto the current gem5
master. I have made sure that they build and run, but haven't done any
extensive testing after rebasing.
The kvm+x86 branch provides basic functionality, such as interfacing
with gem'5 device models and checkpointing. CPU switching works, but
will be unstable due to missing/broken x87/SSE support (mainly missing
fxsave/fxrstor). I have a bunch of x87 in the fixes-x87 [2] branch that
add support for fxsave/fxrstor and fix the load/store instructions. This
is needed for stable switching.
I have tested both normal CPU switching and CPU switching by loading
checkpoints from simulated CPUs directly into the KVM-based CPU. Both
used to work, but I suspect that the latter might be broken due to TLB
checkpointing. Loading the checkpoint is likely to work, but switching
back to a simulated CPU will probably break since the TLB will be stale.
Another issue is the current lack of pseudo inst support. We should
support this without requiring a patched host kernel and preferably
without a patched guest kernel. The approach taken by other KVM-based
software is to use virtual PCI devices. We could do that, but it would
be unnecessarily complicated (requiring PCI interaction in the guest and
potentially making a mess out of the gem5 memory system). The approach
I'm currently using is by (ab)using the support for memory mapped IPRs.
I have a proof-of-concept implementation in the mem-pseudo [3] branch.
On x86, I simply map 0xFFFF0000-0xFFFFFFFF to a magic range of IPRs. A
64-bit read from 0xFFFFxxyy returns the result of a call to m5op
function xx and subfunction.
Both the kvm-x86 branch and the fixes-x87 branch depend on support for
the __float80 type in gcc. I plan to fix that before submitting the
affected changesets for review.
//Andreas
[1] https://github.com/andysan/gem5/tree/kvm-x86
[2] https://github.com/andysan/gem5/tree/fixes-x87
[3] https://github.com/andysan/gem5/tree/mem-pseudo
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