linux-kernel - Re: [PATCH v5 06/10] KVM: selftests: Add NX huge pages test

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Date:   Thu, 14 Apr 2022 13:59:46 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        David Matlack <dmatlack@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Dunn <daviddunn@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Junaid Shahid <junaids@...gle.com>
Subject: Re: [PATCH v5 06/10] KVM: selftests: Add NX huge pages test

On Wed, Apr 13, 2022 at 3:35 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Wed, Apr 13, 2022, Ben Gardon wrote:
> > There's currently no test coverage of NX hugepages in KVM selftests, so
> > add a basic test to ensure that the feature works as intended.
>
> ...
>
> > diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > new file mode 100644
> > index 000000000000..7f80e48781fd
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > @@ -0,0 +1,166 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * tools/testing/selftests/kvm/nx_huge_page_test.c
> > + *
> > + * Usage: to be run via nx_huge_page_test.sh, which does the necessary
> > + * environment setup and teardown
>
> It would be really nice if this test could either (a) do something useful without
> having to manually set /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages,
> or (b) refuse to run unless it's (likely) been invoked by the script.  E.g. maybe
> add a magic token that must be passed in?  That way just running the bare test
> will provide a helpful skip message, but someone that wants to fiddle with it can
> still run it manually.
>
> > +int main(int argc, char **argv)
> > +{
> > +     struct kvm_vm *vm;
> > +     struct timespec ts;
> > +     void *hva;
>
> This needs to check if the workaround is actually enabled via module param.  Not
> as big a deal if there's a magic number, but it's also not too hard to query a
> module param.  Or at least, it shouldn't be, I'm fairly certain that's one of the
> things I want to address in the selftests overhaul.
>
> Aha! Actually, IIUC, the patch that validates the per-VM override adds full support
> for the module param being turned off.
>
> So, how about pull in the tweaks to the expected number to this patch, and then
> the per-VM override test just makes disable_nx a logical OR of the module param
> beyond off or the test using the per-VM override.
>
> > diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> > new file mode 100755
> > index 000000000000..19fc95723fcb
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> > @@ -0,0 +1,25 @@
> > +#!/bin/bash
> > +# SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +# tools/testing/selftests/kvm/nx_huge_page_test.sh
> > +# Copyright (C) 2022, Google LLC.
>
> This should either check for root or use sudo.

Is there not any scenario where the below setup commands could work
without root?

>
> > +NX_HUGE_PAGES=$(cat /sys/module/kvm/parameters/nx_huge_pages)
> > +NX_HUGE_PAGES_RECOVERY_RATIO=$(cat /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio)
> > +NX_HUGE_PAGES_RECOVERY_PERIOD=$(cat /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms)
> > +HUGE_PAGES=$(cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages)
> > +
> > +echo 1 > /sys/module/kvm/parameters/nx_huge_pages
> > +echo 1 > /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio
> > +echo 100 > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
> > +echo 200 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> > +
> > +./nx_huge_pages_test
>
> I would much prefer this find its path and use that to reference the test, e.g. this
> fails if invoking the script from anything but the x86_64 subdirectory.  I'd provide
> a snippet of how to do that, but my scripting skills are garbage :-)
>
> > +RET=$?
> > +
> > +echo $NX_HUGE_PAGES > /sys/module/kvm/parameters/nx_huge_pages
> > +echo $NX_HUGE_PAGES_RECOVERY_RATIO > /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio
> > +echo $NX_HUGE_PAGES_RECOVERY_PERIOD > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
> > +echo $HUGE_PAGES > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> > +
> > +exit $RET
> > --
> > 2.35.1.1178.g4f1659d476-goog
> >