Re: [PATCH v15 00/10] arm64: Add kernel probes (kprobes) support

[William Cohen]

On 07/14/2016 12:22 PM, Catalin Marinas wrote:
> On Fri, Jul 08, 2016 at 12:35:44PM -0400, David Long wrote:
>> David A. Long (3):
>>   arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
>>   arm64: Add more test functions to insn.c
>>   arm64: add conditional instruction simulation support
>>
>> Pratyush Anand (2):
>>   arm64: Blacklist non-kprobe-able symbol
>>   arm64: Treat all entry code as non-kprobe-able
>>
>> Sandeepa Prabhu (4):
>>   arm64: Kprobes with single stepping support
>>   arm64: kprobes instruction simulation support
>>   arm64: Add kernel return probes support (kretprobes)
>>   kprobes: Add arm64 case in kprobe example module
>>
>> William Cohen (1):
>>   arm64: Add trampoline code for kretprobes
> 
> I applied these patches on top of the arm64 for-next/core branch an
> tried to run the resulting kernel in a guest (on a Juno platform using
> both kvmtool and qemu) with KPROBES_SANITY_TEST enabled. Unfortunately,
> the kernel fails to boot with lots of "Unexpected kernel single-step
> exception at EL1".
> 
> Did you manage to run Kprobes in a guest before?
> 

Hi,

I ran the systemtap testsuite several times on a physical machine running a kernel with the kprobe v15 patches without problem. Shouldn't the guest machine behave in the same manner as a host machine for single stepping and exception handling?  If the guest machine is failing, wouldn't that suggest there is a problem with the KVM handling of single stepping for guests?

-Will Cohen