Re: [PATCH v2 1/3] KVM: selftests: Create source of randomness for guest code.

[Sean Christopherson <seanjc@google.com>]

On Thu, Sep 01, 2022, Ricardo Koller wrote:
> On Tue, Aug 30, 2022 at 07:01:57PM +0000, Colton Lewis wrote:
> > David Matlack <dmatlack@google.com> writes:
> > > I think this is broken if !partition_vcpu_memory_access. nr_randoms
> > > (per-vCPU) should be `nr_vcpus * vcpu_memory_bytes >> vm->page_shift`.
> > 
> > 
> > Agree it will break then and should not. But allocating that many more
> > random numbers may eat too much memory. In a test with 64 vcpus, it would
> > try to allocate 64x64 times as many random numbers. I'll try it but may
> > need something different in that case.
> 
> You might want to reconsider the idea of using a random number generator
> inside the guest. IRC the reasons against it were: quality of the random
> numbers, and that some random generators use floating-point numbers. I
> don't think the first one is a big issue. The second one might be an
> issue if we want to generate non-uniform distributions (e.g., poisson);
> but not a problem for now.

I'm pretty I had coded up a pseudo-RNG framework for selftests at one point, but
I cant find the code in my morass of branches and stashes :-(
 
Whatever we do, make sure the randomness and thus any failures are easily
reproducible, i.e. the RNG needs to be seeded pseudo-RNG, not fully random.