Re: [RFC v3 03/10] KVM: PPC: selftests: add support for powerpc

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

sashiko-bot@kernel.org writes:


> commit 4362b48fc35809ad7a74045c726f7ffae0c70ccd
> Author: Nicholas Piggin <npiggin@gmail.com>
>
> KVM: PPC: selftests: add support for powerpc
>
> This commit implements KVM selftests support for powerpc (Book3S-64),
> including ucalls and virtual memory for the radix MMU.
>
>> diff --git a/tools/testing/selftests/kvm/lib/powerpc/processor.c b/tools/testing/selftests/kvm/lib/powerpc/processor.c
>> new file mode 100644
>> index 0000000000000..9846ec26a32aa
>> --- /dev/null
>> +++ b/tools/testing/selftests/kvm/lib/powerpc/processor.c
>
> [ ... ]
>
>> +struct handler {
>> +	void (*fn)(struct ex_regs *regs);
>> +	int trap;
>> +};
>> +
>> +#define NR_HANDLERS	10
>> +static struct handler handlers[NR_HANDLERS];
>
> [Severity: Medium]
> Could this static global array cause state leakage across VMs or race
> conditions in multi-threaded tests?
>
> Since this is defined as a static global on the host rather than a per-VM
> allocation, a new VM will start with a zeroed guest handlers array (from ELF
> loading), but the host's handlers array will retain entries from previous VMs.
>
> This appears to limit the total number of unique handlers that can be installed
> sequentially across all VMs in the entire test process to 10, which would
> eventually result in the "Out of exception handlers" failure below.
>
> Additionally, if multiple threads concurrently create VMs and install exception
> handlers, would they race on this shared host array and sync corrupted state to
> their respective guests?
>

As of now there are no multi-VM tests which creates VMs in parallel.
Also the powerpc exception handler is not used today. It is deferred for
later use when more powerpc specific tests will get added.

If there's ever a need for parallel multi-VM creation, then we can clean
this up.  Even otherwise, I think making it consistent with the other
architectures makes sense (once PowerPC-specific tests get added), so
that too can be deferred until after this base PowerPC KVM selftests
infrastructure lands.

-ritesh