From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41W3GH1RRJzF35L for ; Thu, 19 Jul 2018 02:56:53 +1000 (AEST) Subject: Re: [PATCH v14 20/22] selftests/vm: testcases must restore pkey-permissions To: Ram Pai , shuahkh@osg.samsung.com, linux-kselftest@vger.kernel.org References: <1531835365-32387-1-git-send-email-linuxram@us.ibm.com> <1531835365-32387-21-git-send-email-linuxram@us.ibm.com> Cc: mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, x86@kernel.org, linux-arch@vger.kernel.org, mingo@redhat.com, mhocko@kernel.org, bauerman@linux.vnet.ibm.com, fweimer@redhat.com, msuchanek@suse.de, aneesh.kumar@linux.vnet.ibm.com From: Dave Hansen Message-ID: Date: Wed, 18 Jul 2018 09:56:49 -0700 MIME-Version: 1.0 In-Reply-To: <1531835365-32387-21-git-send-email-linuxram@us.ibm.com> Content-Type: text/plain; charset=utf-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 07/17/2018 06:49 AM, Ram Pai wrote: > Generally the signal handler restores the state of the pkey register > before returning. However there are times when the read/write operation > can legitamely fail without invoking the signal handler. Eg: A > sys_read() operaton to a write-protected page should be disallowed. In > such a case the state of the pkey register is not restored to its > original state. Test cases may not remember to restoring the key > register state. During cleanup generically restore the key permissions. This would, indeed be a good thing to do for a well-behaved application. But, for selftests, why does it matter what state we leave the key in? Doesn't the test itself need to establish permissions? Don't we *do* that at pkey_alloc() anyway? What problem does this solve? > diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c > index 8a6afdd..ea3cf04 100644 > --- a/tools/testing/selftests/vm/protection_keys.c > +++ b/tools/testing/selftests/vm/protection_keys.c > @@ -1476,8 +1476,13 @@ void run_tests_once(void) > pkey_tests[test_nr](ptr, pkey); > dprintf1("freeing test memory: %p\n", ptr); > free_pkey_malloc(ptr); > + > + /* restore the permission on the key after use */ > + pkey_access_allow(pkey); > + pkey_write_allow(pkey); > sys_pkey_free(pkey); > > + > dprintf1("pkey_faults: %d\n", pkey_faults); > dprintf1("orig_pkey_faults: %d\n", orig_pkey_faults);