Supporting KVM_GUESTDBG_BLOCKIRQ or something similar on ARM64

[puranjay at kernel.org]

Hi Everyone,

I work on the BPF JIT for arm64 and regularly use Qemu with gdb for
debugging by single stepping parts of the code. I realized that whenever
I enable KVM, single stepping doesn't work as expected and it lands in an
interrupt handler.

It always worked for me on x86 so I looked in the source code and found
that x86 supports KVM_GUESTDBG_BLOCKIRQ that blocks IRQs when single
stepping.

I assume that arm64 doesn't support KVM_GUESTDBG_BLOCKIRQ because it is
not trivial to implement this on arm64 due to some architectural
limitations? There was a patch [1] posted in 2022 to solve this issue
but it was not merged.

Let's start a discussion about what needs to be done to support this on
arm64.

Thanks,
Puranjay

[1] https://lore.kernel.org/lkml/20221219102452.2860088-2-sumit.garg@linaro.org/
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