linux-kernel - Re: [PATCH] KVM: selftests: Enable USERFAULTFD

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Date:   Mon, 6 Feb 2023 18:15:16 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Oliver Upton <oliver.upton@...ux.dev>
Cc:     Mark Brown <broonie@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        anup@...infault.org
Subject: Re: [PATCH] KVM: selftests: Enable USERFAULTFD

On Mon, Feb 06, 2023, Oliver Upton wrote:
> +cc x86, riscv as they're also affected.
> 
> On Thu, Feb 02, 2023 at 09:01:36PM +0000, Mark Brown wrote:
> > The page_fault_test KVM selftest requires userfaultfd but the config
> > fragment for the KVM selftests does not enable it, meaning that those tests
> > are skipped in CI systems that rely on appropriate settings in the config
> > fragments except on S/390 which happens to have it in defconfig. Enable
> > the option in the config fragment so that the tests get run.

What do CI systems do for HugeTLB and THP?  Those are the other config options I
can think of where there are very interesting interactions from a KVM perspective,
but where KVM doesn't have a strict dependency on the feature.

E.g. x86_64_defconfig selects CONFIG_HUGETLBFS=y, but I don't see anything for THP,
and AFAICT TRANSPARENT_HUGEPAGE is default=n.

> Thanks for catching this.
> 
> I believe we also need UFFD for demand_paging_test, which is used by all
> the KVM selftests arches. I plan on picking this up, but if anyone has
> objections please shout :)

All yours.

Reviewed-by: Sean Christopherson <seanjc@...gle.com>