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Fri, 21 Aug 2020 07:14:54 +0000 (GMT) Received: from [9.102.2.201] (unknown [9.102.2.201]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 21 Aug 2020 07:14:54 +0000 (GMT) Subject: Re: [PATCH v2 07/13] mm/debug_vm_pgtable/set_pte/pmd/pud: Don't use set_*_at to update an existing pte entry To: Christophe Leroy , linux-mm@kvack.org, akpm@linux-foundation.org References: <20200819130107.478414-1-aneesh.kumar@linux.ibm.com> <20200819130107.478414-8-aneesh.kumar@linux.ibm.com> From: "Aneesh Kumar K.V" Message-ID: <3d966519-0a6b-3ccb-fd21-b7f06c8e4df7@linux.ibm.com> Date: Fri, 21 Aug 2020 12:44:53 +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 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-08-21_05:2020-08-19, 2020-08-21 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 phishscore=0 spamscore=0 priorityscore=1501 mlxlogscore=671 impostorscore=0 mlxscore=0 bulkscore=0 clxscore=1015 lowpriorityscore=0 adultscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008210065 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, Anshuman Khandual Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 8/20/20 8:02 PM, Christophe Leroy wrote: > > > Le 19/08/2020 à 15:01, Aneesh Kumar K.V a écrit : >> set_pte_at() should not be used to set a pte entry at locations that >> already holds a valid pte entry. Architectures like ppc64 don't do TLB >> invalidate in set_pte_at() and hence expect it to be used to set >> locations >> that are not a valid PTE. >> >> Signed-off-by: Aneesh Kumar K.V >> --- >>   mm/debug_vm_pgtable.c | 35 +++++++++++++++-------------------- >>   1 file changed, 15 insertions(+), 20 deletions(-) >> >> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c >> index 76f4c713e5a3..9c7e2c9cfc76 100644 >> --- a/mm/debug_vm_pgtable.c >> +++ b/mm/debug_vm_pgtable.c >> @@ -74,15 +74,18 @@ static void __init pte_advanced_tests(struct >> mm_struct *mm, >>   { >>       pte_t pte = pfn_pte(pfn, prot); >> +    /* >> +     * Architectures optimize set_pte_at by avoiding TLB flush. >> +     * This requires set_pte_at to be not used to update an >> +     * existing pte entry. Clear pte before we do set_pte_at >> +     */ >> + >>       pr_debug("Validating PTE advanced\n"); >>       pte = pfn_pte(pfn, prot); >>       set_pte_at(mm, vaddr, ptep, pte); >>       ptep_set_wrprotect(mm, vaddr, ptep); >>       pte = ptep_get(ptep); >>       WARN_ON(pte_write(pte)); >> - >> -    pte = pfn_pte(pfn, prot); >> -    set_pte_at(mm, vaddr, ptep, pte); >>       ptep_get_and_clear(mm, vaddr, ptep); >>       pte = ptep_get(ptep); >>       WARN_ON(!pte_none(pte)); >> @@ -96,13 +99,11 @@ static void __init pte_advanced_tests(struct >> mm_struct *mm, >>       ptep_set_access_flags(vma, vaddr, ptep, pte, 1); >>       pte = ptep_get(ptep); >>       WARN_ON(!(pte_write(pte) && pte_dirty(pte))); >> - >> -    pte = pfn_pte(pfn, prot); >> -    set_pte_at(mm, vaddr, ptep, pte); >>       ptep_get_and_clear_full(mm, vaddr, ptep, 1); >>       pte = ptep_get(ptep); >>       WARN_ON(!pte_none(pte)); >> +    pte = pfn_pte(pfn, prot); >>       pte = pte_mkyoung(pte); >>       set_pte_at(mm, vaddr, ptep, pte); >>       ptep_test_and_clear_young(vma, vaddr, ptep); >> @@ -164,9 +165,6 @@ static void __init pmd_advanced_tests(struct >> mm_struct *mm, >>       pmdp_set_wrprotect(mm, vaddr, pmdp); >>       pmd = READ_ONCE(*pmdp); >>       WARN_ON(pmd_write(pmd)); >> - >> -    pmd = pmd_mkhuge(pfn_pmd(pfn, prot)); >> -    set_pmd_at(mm, vaddr, pmdp, pmd); >>       pmdp_huge_get_and_clear(mm, vaddr, pmdp); >>       pmd = READ_ONCE(*pmdp); >>       WARN_ON(!pmd_none(pmd)); >> @@ -180,13 +178,11 @@ static void __init pmd_advanced_tests(struct >> mm_struct *mm, >>       pmdp_set_access_flags(vma, vaddr, pmdp, pmd, 1); >>       pmd = READ_ONCE(*pmdp); >>       WARN_ON(!(pmd_write(pmd) && pmd_dirty(pmd))); >> - >> -    pmd = pmd_mkhuge(pfn_pmd(pfn, prot)); >> -    set_pmd_at(mm, vaddr, pmdp, pmd); >>       pmdp_huge_get_and_clear_full(vma, vaddr, pmdp, 1); >>       pmd = READ_ONCE(*pmdp); >>       WARN_ON(!pmd_none(pmd)); >> +    pmd = pmd_mkhuge(pfn_pmd(pfn, prot)); >>       pmd = pmd_mkyoung(pmd); >>       set_pmd_at(mm, vaddr, pmdp, pmd); >>       pmdp_test_and_clear_young(vma, vaddr, pmdp); >> @@ -283,18 +279,10 @@ static void __init pud_advanced_tests(struct >> mm_struct *mm, >>       WARN_ON(pud_write(pud)); >>   #ifndef __PAGETABLE_PMD_FOLDED > > Same as below, once set_put_at() is gone, I don't think this #ifndef > __PAGETABLE_PMD_FOLDED is still need, should be possible to replace by > 'if (mm_pmd_folded())' I would skip that change in this series because I still haven't worked out what it means to have FOLDED PMD with CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD. We should probably push that as a cleanup later and somebody who can test that config can do that? Currently i can't boot ppc64 with DBUG_VM_PGTABLE enabled on ppc64 because it is all buggy w.r.t rules. -aneesh