Re: [PATCH v5] selftests/vm: Only run 128TBswitch with 5-level paging

From: Adam Sindelar <adam@wowsignal.io>
To: David Vernet <void@manifault.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, Adam Sindelar <ats@fb.com>,
	kernel-team@fb.com
Subject: Re: [PATCH v5] selftests/vm: Only run 128TBswitch with 5-level paging
Date: Fri, 1 Jul 2022 18:32:17 +0200	[thread overview]
Message-ID: <Yr8hkYbjKaBrRfTx@debian> (raw)
In-Reply-To: <20220701142113.w3vx67s7frkfwwiv@dev0025.ash9.facebook.com>

On Fri, Jul 01, 2022 at 07:21:13AM -0700, David Vernet wrote:
> On Fri, Jul 01, 2022 at 12:49:34PM +0200, Adam Sindelar wrote:
> 
> Hi Adam,
> 
> > The test va_128TBswitch.c expects to be able to pass mmap an address hint
> > and length that cross the address 1<<47. On x86_64, this is not possible
> > without 5-level page tables, so the test fails.
> > 
> > The test is already only run on 64-bit powerpc and x86_64 archs, but this
> > patch adds an additional check on x86_64 that skips the test if PG_TABLE_LEVELS
> 
> It looks like checkpatch.pl is complaining about this line being too long:
> 
> WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
> #11:
> patch adds an additional check on x86_64 that skips the test if PG_TABLE_LEVELS
> 

Fixed in v6, sorry.

> > < 5.  There is precedent for checking /proc/config.gz in selftests, e.g. in
> > selftests/firmware.
> > 
> > Running the tests produces the desired output:
> > 
> > sudo make -C tools/testing/selftests TARGETS=vm run_tests
> > ---------------------------
> > running ./va_128TBswitch.sh
> > ---------------------------
> > ./va_128TBswitch.sh: PG_TABLE_LEVELS=4, must be >= 5 to run this test
> > [SKIP]
> > -------------------------------
> > 
> > Signed-off-by: Adam Sindelar <adam@wowsignal.io>
> > ---
> > V4 -> V5: Renamed "die" to "fail" (missed the review comment, sorry!)
> > V3 -> V4: Restrict the check to x86_64
> > V2 -> V3: Clean up the commit message
> > V1 -> V2: Variables local, fixed Makefile typo, comment on gzip usage
> > 
> >  tools/testing/selftests/vm/Makefile          |  1 +
> >  tools/testing/selftests/vm/run_vmtests.sh    |  2 +-
> >  tools/testing/selftests/vm/va_128TBswitch.sh | 54 ++++++++++++++++++++
> >  3 files changed, 56 insertions(+), 1 deletion(-)
> >  create mode 100755 tools/testing/selftests/vm/va_128TBswitch.sh
> 
> [...]
> 
> > diff --git a/tools/testing/selftests/vm/va_128TBswitch.sh b/tools/testing/selftests/vm/va_128TBswitch.sh
> > new file mode 100755
> > index 000000000000..334d12715ac3
> > --- /dev/null
> > +++ b/tools/testing/selftests/vm/va_128TBswitch.sh
> > @@ -0,0 +1,54 @@
> > +#!/bin/bash
> > +# SPDX-License-Identifier: GPL-2.0
> > +#
> > +# Copyright (C) 2022 Adam Sindelar (Meta) <adam@wowsignal.io>
> > +#
> > +# This is a test for mmap behavior with 5-level paging. This script wraps the
> > +# real test to check that the kernel is configured to support at least 5
> > +# pagetable levels.
> > +
> > +# 1 means the test failed
> > +exitcode=1
> > +
> > +# Kselftest framework requirement - SKIP code is 4.
> > +ksft_skip=4
> > +
> > +fail()
> > +{
> > +    echo "$1"
> > +    exit $exitcode
> > +}
> 
> My apologies for missing this in earlier reviews, but this file should be
> updated to use 8-character wide tabs instead of spaces. Please see [0] for
> details.
> 
> [0] https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
> 

Ah, sorry, I thought that only applied to C code, but now I see
shellscripts are formatted the same way. I'll fix my editor config.

> > +
> > +check_supported_x86_64()
> > +{
> > +    local config="/proc/config.gz"
> > +    [[ -f "${config}" ]] || config="/boot/config-$(uname -r)"
> > +    [[ -f "${config}" ]] || fail "Cannot find kernel config in /proc or /boot"
> > +
> > +    # gzip -dcfq automatically handles both compressed and plaintext input.
> > +    # See man 1 gzip under '-f'.
> > +    local pg_table_levels=$(gzip -dcfq "${config}" | grep PGTABLE_LEVELS | cut -d'=' -f 2)
> > +
> > +    if [[ "${pg_table_levels}" -lt 5 ]]; then
> > +        echo "$0: PGTABLE_LEVELS=${pg_table_levels}, must be >= 5 to run this test"
> > +        exit $ksft_skip
> > +    fi
> > +}
> > +
> > +check_test_requirements()
> > +{
> > +    # The test supports x86_64 and powerpc64. We currently have no useful
> > +    # eligibility check for powerpc64, and the test itself will reject other
> > +    # architectures.
> > +    case `uname -m` in
> > +        "x86_64")
> > +            check_supported_x86_64
> > +        ;;
> > +        *)
> > +            return 0
> > +        ;;
> > +    esac
> > +}
> > +
> > +check_test_requirements
> > +./va_128TBswitch
> > -- 
> > 2.35.1
> > 