linux-kernel - Re: [PATCH v4 2/2] selftests: KVM: Add dirty logging page splitting test

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Date:   Thu, 26 Jan 2023 12:06:10 -0800
From:   Vipin Sharma <vipinsh@...gle.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>
Subject: Re: [PATCH v4 2/2] selftests: KVM: Add dirty logging page splitting test

On Wed, Jan 25, 2023 at 10:23 AM Ben Gardon <bgardon@...gle.com> wrote:

> +static void run_vcpus_get_page_stats(struct kvm_vm *vm, struct kvm_page_stats *stats, const char *stage)
> +{
> +       int i;
> +
> +       iteration++;
> +       for (i = 0; i < VCPUS; i++) {
> +               while (READ_ONCE(vcpu_last_completed_iteration[i]) !=
> +                      iteration)
> +                       ;
> +       }
> +
> +       get_page_stats(vm, stats, stage);

get_page_stats() is already called in run_test() explicitly for other
stats. I think it's better to split this function and make the flow
like:

run_vcpus_till_iteration(iteration++);
get_page_stats(vm, &stats_populated, "populating memory");

This makes it easy to follow run_test_till_iteration() and easy to see
where stats are collected. run_test_till_iteration() can also be a
library function used by other tests like dirty_log_perf_test

> +       dirty_log_manual_caps = 0;
> +       for_each_guest_mode(run_test, NULL);
> +
> +       dirty_log_manual_caps =
> +               kvm_check_cap(KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
> +
> +       if (dirty_log_manual_caps) {
> +               dirty_log_manual_caps &= (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE |
> +                                         KVM_DIRTY_LOG_INITIALLY_SET);
> +               for_each_guest_mode(run_test, NULL);
> +       }

Should there be a message to show  that this capability is not tested
as it is not available?
Or, there can be a command line option to explicitly provide intent of
testing combined,  split modes, or both? Then test can error out
accordingly.