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Mon, 13 Nov 2023 15:46:30 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 32C052004B; Mon, 13 Nov 2023 15:46:30 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 30AF020040; Mon, 13 Nov 2023 15:46:29 +0000 (GMT) Received: from [9.43.73.221] (unknown [9.43.73.221]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 13 Nov 2023 15:46:28 +0000 (GMT) Message-ID: <4faeb598-87b1-4aca-90cb-3890f95ae7b6@linux.ibm.com> Date: Mon, 13 Nov 2023 21:16:28 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] powerpc/book3s/hash: Drop _PAGE_PRIVILEGED from PAGE_NONE Content-Language: en-US To: Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au, christophe.leroy@csgroup.eu References: <20231102132327.294050-1-aneesh.kumar@linux.ibm.com> <02b602c0-2b40-4cf9-b0ca-4bc12ac267cd@linux.ibm.com> From: Aneesh Kumar K V In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: Wi3kZU4EC35coKf-S0myeYCIOh0oRC8Y X-Proofpoint-ORIG-GUID: 5D-QKTgZhs3Zen8KSbh9_GJs7twKl-h9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.987,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-11-13_06,2023-11-09_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 bulkscore=0 suspectscore=0 adultscore=0 priorityscore=1501 spamscore=0 mlxlogscore=857 lowpriorityscore=0 phishscore=0 mlxscore=0 malwarescore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311060000 definitions=main-2311130128 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: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 11/13/23 5:17 PM, Nicholas Piggin wrote: > On Mon Nov 13, 2023 at 8:45 PM AEST, Aneesh Kumar K V wrote: .... >>>> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c >>>> index ad2afa08e62e..b2eda22195f0 100644 >>>> --- a/arch/powerpc/mm/book3s64/hash_utils.c >>>> +++ b/arch/powerpc/mm/book3s64/hash_utils.c >>>> @@ -310,9 +310,26 @@ unsigned long htab_convert_pte_flags(unsigned long pteflags, unsigned long flags >>>> else >>>> rflags |= 0x3; >>>> } >>>> + WARN_ON(!(pteflags & _PAGE_RWX)); >>>> } else { >>>> if (pteflags & _PAGE_RWX) >>>> rflags |= 0x2; >>>> + else { >>>> + /* >>>> + * PAGE_NONE will get mapped to 0b110 (slb key 1 no access) >>>> + * We picked 0b110 instead of 0b000 so that slb key 0 will >>>> + * get only read only access for the same rflags. >>>> + */ >>>> + if (mmu_has_feature(MMU_FTR_KERNEL_RO)) >>>> + rflags |= (HPTE_R_PP0 | 0x2); >>>> + /* >>>> + * rflags = HPTE_R_N >>>> + * Without KERNEL_RO feature this will result in slb >>>> + * key 0 with read/write. But ISA only supports that. >>>> + * There is no key 1 no-access and key 0 read-only >>>> + * pp bit support. >>>> + */ >>>> + } >>>> if (!((pteflags & _PAGE_WRITE) && (pteflags & _PAGE_DIRTY))) >>>> rflags |= 0x1; >>>> } >>> >> >> V2 is also dropping the above change, because we will never have hash table entries inserted. >> >> This is added to commit message. >> >> Hash fault handling code did get some WARN_ON added because those >> functions are not expected to get called with _PAGE_READ cleared. >> commit 18061c17c8ec ("powerpc/mm: Update PROTFAULT handling in the page fault path") >> explains the details. > > Should it be a WARN_ON_ONCE? Any useful way to recover from it? Could > the added WARN come with some comments from that commit that explain > it? > This should never happen unless someone messed up check_pte_access(). The WARN_ON() is a way to remind me not to add no access ppp mapping in the htab_convert_pte_flags() as I did above. Initially I was planning to add only a comment, but then in the rare case of we getting it wrong it is nice to do a console log. -aneesh