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Tue, 1 Sep 2020 09:58:30 +0000 (GMT) Received: from [9.85.87.174] (unknown [9.85.87.174]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 1 Sep 2020 09:58:30 +0000 (GMT) Subject: Re: [PATCH v3 13/13] mm/debug_vm_pgtable: populate a pte entry before fetching it To: Anshuman Khandual , linux-mm@kvack.org, akpm@linux-foundation.org Cc: mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-snps-arc@lists.infradead.org, x86@kernel.org, linux-arch@vger.kernel.org, Gerald Schaefer , Christophe Leroy , Vineet Gupta , Mike Rapoport , Qian Cai References: <20200827080438.315345-1-aneesh.kumar@linux.ibm.com> <20200827080438.315345-14-aneesh.kumar@linux.ibm.com> From: "Aneesh Kumar K.V" Message-ID: <7ef7c302-e7e6-570e-3100-5dd1bf9551be@linux.ibm.com> Date: Tue, 1 Sep 2020 15:28:29 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-01_04:2020-09-01,2020-09-01 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 spamscore=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 bulkscore=0 clxscore=1015 adultscore=0 priorityscore=1501 mlxlogscore=999 mlxscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009010080 X-Rspamd-Queue-Id: 6289C28A4E8 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/1/20 1:08 PM, Anshuman Khandual wrote: >=20 >=20 > On 09/01/2020 12:07 PM, Aneesh Kumar K.V wrote: >> On 9/1/20 8:55 AM, Anshuman Khandual wrote: >>> >>> >>> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote: >>>> pte_clear_tests operate on an existing pte entry. Make sure that is = not a none >>>> pte entry. >>>> >>>> Signed-off-by: Aneesh Kumar K.V >>>> --- >>>> =C2=A0 mm/debug_vm_pgtable.c | 6 ++++-- >>>> =C2=A0 1 file changed, 4 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c >>>> index 21329c7d672f..8527ebb75f2c 100644 >>>> --- a/mm/debug_vm_pgtable.c >>>> +++ b/mm/debug_vm_pgtable.c >>>> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_= struct *mm, pgd_t *pgdp, >>>> =C2=A0 static void __init pte_clear_tests(struct mm_struct *mm, pte= _t *ptep, >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unsigned long vaddr) >>>> =C2=A0 { >>>> -=C2=A0=C2=A0=C2=A0 pte_t pte =3D ptep_get(ptep); >>>> +=C2=A0=C2=A0=C2=A0 pte_t pte =3D=C2=A0 ptep_get_and_clear(mm, vaddr= , ptep); >>> >>> Seems like ptep_get_and_clear() here just clears the entry in prepara= tion >>> for a following set_pte_at() which otherwise would have been a proble= m on >>> ppc64 as you had pointed out earlier i.e set_pte_at() should not upda= te an >>> existing valid entry. So the commit message here is bit misleading. >>> >> >> and also fetch the pte value which is used further. >> >> >>>> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pr_debug("Validating PTE clea= r\n"); >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pte =3D __pte(pte_val(pte) | RANDOM_= ORVALUE); >>>> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void) >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 p4d_t *p4dp, *saved_p4dp; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pud_t *pudp, *saved_pudp; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pmd_t *pmdp, *saved_pmdp, pmd; >>>> -=C2=A0=C2=A0=C2=A0 pte_t *ptep; >>>> +=C2=A0=C2=A0=C2=A0 pte_t *ptep, pte; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pgtable_t saved_ptep; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pgprot_t prot, protnone; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 phys_addr_t paddr; >>>> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void) >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >>>> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ptep =3D pte_alloc_map_lock(m= m, pmdp, vaddr, &ptl); >>>> +=C2=A0=C2=A0=C2=A0 pte =3D pfn_pte(pte_aligned, prot); >>>> +=C2=A0=C2=A0=C2=A0 set_pte_at(mm, vaddr, ptep, pte); >>> >>> Not here, creating and populating an entry must be done in respective >>> test functions itself. Besides, this seems bit redundant as well. The >>> test pte_clear_tests() with the above change added, already >>> >>> - Clears the PTEP entry with ptep_get_and_clear() >> >> and fetch the old value set previously. >=20 > In that case, please move above two lines i.e >=20 > pte =3D pfn_pte(pte_aligned, prot); > set_pte_at(mm, vaddr, ptep, pte); >=20 > from debug_vm_pgtable() to pte_clear_tests() and update it's arguments > as required. >=20 Frankly, I don't understand what these tests are testing. It all looks=20 like some random clear and set. static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep, unsigned long vaddr, unsigned long pfn, pgprot_t prot) { pte_t pte =3D pfn_pte(pfn, prot); set_pte_at(mm, vaddr, ptep, pte); pte =3D ptep_get_and_clear(mm, vaddr, ptep); pr_debug("Validating PTE clear\n"); pte =3D __pte(pte_val(pte) | RANDOM_ORVALUE); set_pte_at(mm, vaddr, ptep, pte); barrier(); pte_clear(mm, vaddr, ptep); pte =3D ptep_get(ptep); WARN_ON(!pte_none(pte)); } -aneesh