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Tue, 8 Sep 2020 12:09:03 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 98841AE051; Tue, 8 Sep 2020 12:09:01 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.146.40]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 8 Sep 2020 12:09:01 +0000 (GMT) Subject: Re: [RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table folding To: Christophe Leroy , Gerald Schaefer , Jason Gunthorpe , John Hubbard Cc: Peter Zijlstra , Dave Hansen , linux-mm , Paul Mackerras , linux-sparc , Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-arch , linux-s390 , Vasily Gorbik , Richard Weinberger , linux-x86 , Russell King , Ingo Molnar , Catalin Marinas , Andrey Ryabinin , Heiko Carstens , Arnd Bergmann , Jeff Dike , linux-um , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , linux-arm , linux-power , LKML , Andrew Morton , Linus Torvalds , Mike Rapoport References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com> <20200907180058.64880-2-gerald.schaefer@linux.ibm.com> <82fbe8f9-f199-5fc2-4168-eb43ad0b0346@csgroup.eu> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 In-Reply-To: <82fbe8f9-f199-5fc2-4168-eb43ad0b0346@csgroup.eu> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-TM-AS-GCONF: 00 Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-08_06:2020-09-08,2020-09-08 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 bulkscore=0 clxscore=1011 mlxlogscore=999 adultscore=0 phishscore=0 priorityscore=1501 suspectscore=0 lowpriorityscore=0 malwarescore=0 spamscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009080108 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08.09.20 07:06, Christophe Leroy wrote: > > > Le 07/09/2020 à 20:00, Gerald Schaefer a écrit : >> From: Alexander Gordeev >> >> Commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast >> code") introduced a subtle but severe bug on s390 with gup_fast, due to >> dynamic page table folding. >> >> The question "What would it require for the generic code to work for s390" >> has already been discussed here >> https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 >> and ended with a promising approach here >> https://lkml.kernel.org/r/20190419153307.4f2911b5@mschwideX1 >> which in the end unfortunately didn't quite work completely. >> >> We tried to mimic static level folding by changing pgd_offset to always >> calculate top level page table offset, and do nothing in folded pXd_offset. >> What has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end do >> not reflect this dynamic behaviour, and still act like static 5-level >> page tables. >> > > [...] > >> >> Fix this by introducing new pXd_addr_end_folded helpers, which take an >> additional pXd entry value parameter, that can be used on s390 >> to determine the correct page table level and return corresponding >> end / boundary. With that, the pointer iteration will always >> happen in gup_pgd_range for s390. No change for other architectures >> introduced. > > Not sure pXd_addr_end_folded() is the best understandable name, allthough I don't have any alternative suggestion at the moment. > Maybe could be something like pXd_addr_end_fixup() as it will disappear in the next patch, or pXd_addr_end_gup() ? > > Also, if it happens to be acceptable to get patch 2 in stable, I think you should switch patch 1 and patch 2 to avoid the step through pXd_addr_end_folded() given that this fixes a data corruption issue, wouldnt it be the best to go forward with this patch ASAP and then handle the other patches on top with all the time that we need? > > >> >> Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") >> Cc: # 5.2+ >> Reviewed-by: Gerald Schaefer >> Signed-off-by: Alexander Gordeev >> Signed-off-by: Gerald Schaefer >> --- >>   arch/s390/include/asm/pgtable.h | 42 +++++++++++++++++++++++++++++++++ >>   include/linux/pgtable.h         | 16 +++++++++++++ >>   mm/gup.c                        |  8 +++---- >>   3 files changed, 62 insertions(+), 4 deletions(-) >> >> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h >> index 7eb01a5459cd..027206e4959d 100644 >> --- a/arch/s390/include/asm/pgtable.h >> +++ b/arch/s390/include/asm/pgtable.h >> @@ -512,6 +512,48 @@ static inline bool mm_pmd_folded(struct mm_struct *mm) >>   } >>   #define mm_pmd_folded(mm) mm_pmd_folded(mm) >>   +/* >> + * With dynamic page table levels on s390, the static pXd_addr_end() functions >> + * will not return corresponding dynamic boundaries. This is no problem as long >> + * as only pXd pointers are passed down during page table walk, because >> + * pXd_offset() will simply return the given pointer for folded levels, and the >> + * pointer iteration over a range simply happens at the correct page table >> + * level. >> + * It is however a problem with gup_fast, or other places walking the page >> + * tables w/o locks using READ_ONCE(), and passing down the pXd values instead >> + * of pointers. In this case, the pointer given to pXd_offset() is a pointer to >> + * a stack variable, which cannot be used for pointer iteration at the correct >> + * level. Instead, the iteration then has to happen by going up to pgd level >> + * again. To allow this, provide pXd_addr_end_folded() functions with an >> + * additional pXd value parameter, which can be used on s390 to determine the >> + * folding level and return the corresponding boundary. >> + */ >> +static inline unsigned long rste_addr_end_folded(unsigned long rste, unsigned long addr, unsigned long end) > > What does 'rste' stands for ? > > Isn't this line a bit long ? this is region/segment table entry according to the architecture. On our platform we do have the pagetables with a different format that next levels (segment table -> 1MB granularity, region 3rd table -> 2 GB granularity, region 2nd table -> 4TB granularity, region 1st table -> 8 PB granularity. ST,R3,R2,R1 have the same format and are thus often called crste (combined region and segment table entry). From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Date: Tue, 08 Sep 2020 12:09:01 +0000 Subject: Re: [RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table folding Message-Id: <70a3dcb5-5ed1-6efa-6158-d0573d6927da@de.ibm.com> List-Id: References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com> <20200907180058.64880-2-gerald.schaefer@linux.ibm.com> <82fbe8f9-f199-5fc2-4168-eb43ad0b0346@csgroup.eu> In-Reply-To: <82fbe8f9-f199-5fc2-4168-eb43ad0b0346@csgroup.eu> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Christophe Leroy , Gerald Schaefer , Jason Gunthorpe , John Hubbard Cc: Peter Zijlstra , Dave Hansen , linux-mm , Paul Mackerras , linux-sparc , Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-arch , linux-s390 , Vasily Gorbik , Richard Weinberger , linux-x86 , Russell King , Ingo Molnar , Catalin Marinas , Andrey Ryabinin , Heiko Carstens , Arnd Bergmann , Jeff Dike , linux-um , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , linux-arm , linux-power , LKML , Andrew Morton , Linus Torvalds , Mike Rapoport On 08.09.20 07:06, Christophe Leroy wrote: > > > Le 07/09/2020 à 20:00, Gerald Schaefer a écrit : >> From: Alexander Gordeev >> >> Commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast >> code") introduced a subtle but severe bug on s390 with gup_fast, due to >> dynamic page table folding. >> >> The question "What would it require for the generic code to work for s390" >> has already been discussed here >> https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 >> and ended with a promising approach here >> https://lkml.kernel.org/r/20190419153307.4f2911b5@mschwideX1 >> which in the end unfortunately didn't quite work completely. >> >> We tried to mimic static level folding by changing pgd_offset to always >> calculate top level page table offset, and do nothing in folded pXd_offset. >> What has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end do >> not reflect this dynamic behaviour, and still act like static 5-level >> page tables. >> > > [...] > >> >> Fix this by introducing new pXd_addr_end_folded helpers, which take an >> additional pXd entry value parameter, that can be used on s390 >> to determine the correct page table level and return corresponding >> end / boundary. With that, the pointer iteration will always >> happen in gup_pgd_range for s390. No change for other architectures >> introduced. > > Not sure pXd_addr_end_folded() is the best understandable name, allthough I don't have any alternative suggestion at the moment. > Maybe could be something like pXd_addr_end_fixup() as it will disappear in the next patch, or pXd_addr_end_gup() ? > > Also, if it happens to be acceptable to get patch 2 in stable, I think you should switch patch 1 and patch 2 to avoid the step through pXd_addr_end_folded() given that this fixes a data corruption issue, wouldnt it be the best to go forward with this patch ASAP and then handle the other patches on top with all the time that we need? > > >> >> Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") >> Cc: # 5.2+ >> Reviewed-by: Gerald Schaefer >> Signed-off-by: Alexander Gordeev >> Signed-off-by: Gerald Schaefer >> --- >>   arch/s390/include/asm/pgtable.h | 42 +++++++++++++++++++++++++++++++++ >>   include/linux/pgtable.h         | 16 +++++++++++++ >>   mm/gup.c                        |  8 +++---- >>   3 files changed, 62 insertions(+), 4 deletions(-) >> >> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h >> index 7eb01a5459cd..027206e4959d 100644 >> --- a/arch/s390/include/asm/pgtable.h >> +++ b/arch/s390/include/asm/pgtable.h >> @@ -512,6 +512,48 @@ static inline bool mm_pmd_folded(struct mm_struct *mm) >>   } >>   #define mm_pmd_folded(mm) mm_pmd_folded(mm) >>   +/* >> + * With dynamic page table levels on s390, the static pXd_addr_end() functions >> + * will not return corresponding dynamic boundaries. This is no problem as long >> + * as only pXd pointers are passed down during page table walk, because >> + * pXd_offset() will simply return the given pointer for folded levels, and the >> + * pointer iteration over a range simply happens at the correct page table >> + * level. >> + * It is however a problem with gup_fast, or other places walking the page >> + * tables w/o locks using READ_ONCE(), and passing down the pXd values instead >> + * of pointers. In this case, the pointer given to pXd_offset() is a pointer to >> + * a stack variable, which cannot be used for pointer iteration at the correct >> + * level. Instead, the iteration then has to happen by going up to pgd level >> + * again. To allow this, provide pXd_addr_end_folded() functions with an >> + * additional pXd value parameter, which can be used on s390 to determine the >> + * folding level and return the corresponding boundary. >> + */ >> +static inline unsigned long rste_addr_end_folded(unsigned long rste, unsigned long addr, unsigned long end) > > What does 'rste' stands for ? > > Isn't this line a bit long ? this is region/segment table entry according to the architecture. On our platform we do have the pagetables with a different format that next levels (segment table -> 1MB granularity, region 3rd table -> 2 GB granularity, region 2nd table -> 4TB granularity, region 1st table -> 8 PB granularity. ST,R3,R2,R1 have the same format and are thus often called crste (combined region and segment table entry). 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 In-Reply-To: <82fbe8f9-f199-5fc2-4168-eb43ad0b0346@csgroup.eu> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-TM-AS-GCONF: 00 Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-09-08_06:2020-09-08, 2020-09-08 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 bulkscore=0 clxscore=1011 mlxlogscore=999 adultscore=0 phishscore=0 priorityscore=1501 suspectscore=0 lowpriorityscore=0 malwarescore=0 spamscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009080108 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: Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-mm , Paul Mackerras , linux-sparc , Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-arch , linux-s390 , Vasily Gorbik , Richard Weinberger , linux-x86 , Russell King , Ingo Molnar , Andrey Ryabinin , Jeff Dike , Arnd Bergmann , Heiko Carstens , linux-um , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , linux-arm , Linus Torvalds , LKML , Andrew Morton , linux-power , Mike Rapoport Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 08.09.20 07:06, Christophe Leroy wrote: > > > Le 07/09/2020 à 20:00, Gerald Schaefer a écrit : >> From: Alexander Gordeev >> >> Commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast >> code") introduced a subtle but severe bug on s390 with gup_fast, due to >> dynamic page table folding. >> >> The question "What would it require for the generic code to work for s390" >> has already been discussed here >> https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 >> and ended with a promising approach here >> https://lkml.kernel.org/r/20190419153307.4f2911b5@mschwideX1 >> which in the end unfortunately didn't quite work completely. >> >> We tried to mimic static level folding by changing pgd_offset to always >> calculate top level page table offset, and do nothing in folded pXd_offset. >> What has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end do >> not reflect this dynamic behaviour, and still act like static 5-level >> page tables. >> > > [...] > >> >> Fix this by introducing new pXd_addr_end_folded helpers, which take an >> additional pXd entry value parameter, that can be used on s390 >> to determine the correct page table level and return corresponding >> end / boundary. With that, the pointer iteration will always >> happen in gup_pgd_range for s390. No change for other architectures >> introduced. > > Not sure pXd_addr_end_folded() is the best understandable name, allthough I don't have any alternative suggestion at the moment. > Maybe could be something like pXd_addr_end_fixup() as it will disappear in the next patch, or pXd_addr_end_gup() ? > > Also, if it happens to be acceptable to get patch 2 in stable, I think you should switch patch 1 and patch 2 to avoid the step through pXd_addr_end_folded() given that this fixes a data corruption issue, wouldnt it be the best to go forward with this patch ASAP and then handle the other patches on top with all the time that we need? > > >> >> Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") >> Cc: # 5.2+ >> Reviewed-by: Gerald Schaefer >> Signed-off-by: Alexander Gordeev >> Signed-off-by: Gerald Schaefer >> --- >>   arch/s390/include/asm/pgtable.h | 42 +++++++++++++++++++++++++++++++++ >>   include/linux/pgtable.h         | 16 +++++++++++++ >>   mm/gup.c                        |  8 +++---- >>   3 files changed, 62 insertions(+), 4 deletions(-) >> >> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h >> index 7eb01a5459cd..027206e4959d 100644 >> --- a/arch/s390/include/asm/pgtable.h >> +++ b/arch/s390/include/asm/pgtable.h >> @@ -512,6 +512,48 @@ static inline bool mm_pmd_folded(struct mm_struct *mm) >>   } >>   #define mm_pmd_folded(mm) mm_pmd_folded(mm) >>   +/* >> + * With dynamic page table levels on s390, the static pXd_addr_end() functions >> + * will not return corresponding dynamic boundaries. This is no problem as long >> + * as only pXd pointers are passed down during page table walk, because >> + * pXd_offset() will simply return the given pointer for folded levels, and the >> + * pointer iteration over a range simply happens at the correct page table >> + * level. >> + * It is however a problem with gup_fast, or other places walking the page >> + * tables w/o locks using READ_ONCE(), and passing down the pXd values instead >> + * of pointers. In this case, the pointer given to pXd_offset() is a pointer to >> + * a stack variable, which cannot be used for pointer iteration at the correct >> + * level. Instead, the iteration then has to happen by going up to pgd level >> + * again. To allow this, provide pXd_addr_end_folded() functions with an >> + * additional pXd value parameter, which can be used on s390 to determine the >> + * folding level and return the corresponding boundary. >> + */ >> +static inline unsigned long rste_addr_end_folded(unsigned long rste, unsigned long addr, unsigned long end) > > What does 'rste' stands for ? > > Isn't this line a bit long ? this is region/segment table entry according to the architecture. On our platform we do have the pagetables with a different format that next levels (segment table -> 1MB granularity, region 3rd table -> 2 GB granularity, region 2nd table -> 4TB granularity, region 1st table -> 8 PB granularity. ST,R3,R2,R1 have the same format and are thus often called crste (combined region and segment table entry). 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Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-mm , Paul Mackerras , linux-sparc , Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-arch , linux-s390 , Vasily Gorbik , Richard Weinberger , linux-x86 , Russell King , Ingo Molnar , Andrey Ryabinin , Jeff Dike , Arnd Bergmann , Heiko Carstens , linux-um , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , linux-arm , Linus Torvalds , LKML , Andrew Morton , linux-power , Mike Rapoport Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org CgpPbiAwOC4wOS4yMCAwNzowNiwgQ2hyaXN0b3BoZSBMZXJveSB3cm90ZToKPiAKPiAKPiBMZSAw Ny8wOS8yMDIwIMOgIDIwOjAwLCBHZXJhbGQgU2NoYWVmZXIgYSDDqWNyaXTCoDoKPj4gRnJvbTog QWxleGFuZGVyIEdvcmRlZXYgPGFnb3JkZWV2QGxpbnV4LmlibS5jb20+Cj4+Cj4+IENvbW1pdCAx 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X19fX19fX19fX19fX19fX19fX19fX19fCmxpbnV4LWFybS1rZXJuZWwgbWFpbGluZyBsaXN0Cmxp bnV4LWFybS1rZXJuZWxAbGlzdHMuaW5mcmFkZWFkLm9yZwpodHRwOi8vbGlzdHMuaW5mcmFkZWFk Lm9yZy9tYWlsbWFuL2xpc3RpbmZvL2xpbnV4LWFybS1rZXJuZWwK From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table folding References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com> <20200907180058.64880-2-gerald.schaefer@linux.ibm.com> <82fbe8f9-f199-5fc2-4168-eb43ad0b0346@csgroup.eu> From: Christian Borntraeger Message-ID: <70a3dcb5-5ed1-6efa-6158-d0573d6927da@de.ibm.com> Date: Tue, 8 Sep 2020 14:09:01 +0200 In-Reply-To: <82fbe8f9-f199-5fc2-4168-eb43ad0b0346@csgroup.eu> Content-Language: en-US MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Christophe Leroy , Gerald Schaefer , Jason Gunthorpe , John Hubbard Cc: Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-mm , Paul Mackerras , linux-sparc , Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-arch , linux-s390 , Vasily Gorbik , Richard Weinberger , linux-x86 , Russell King , Ingo Molnar , Andrey Ryabinin , Jeff Dike , Arnd Bergmann , Heiko Carstens , linux-um , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , linux-arm , Linus Torvalds , LKML , Andrew Morton , linux-power , Mike Rapoport CgpPbiAwOC4wOS4yMCAwNzowNiwgQ2hyaXN0b3BoZSBMZXJveSB3cm90ZToKPiAKPiAKPiBMZSAw Ny8wOS8yMDIwIMOgIDIwOjAwLCBHZXJhbGQgU2NoYWVmZXIgYSDDqWNyaXTCoDoKPj4gRnJvbTog QWxleGFuZGVyIEdvcmRlZXYgPGFnb3JkZWV2QGxpbnV4LmlibS5jb20+Cj4+Cj4+IENvbW1pdCAx YTQyMDEwY2RjMjYgKCJzMzkwL21tOiBjb252ZXJ0IHRvIHRoZSBnZW5lcmljIGdldF91c2VyX3Bh Z2VzX2Zhc3QKPj4gY29kZSIpIGludHJvZHVjZWQgYSBzdWJ0bGUgYnV0IHNldmVyZSBidWcgb24g czM5MCB3aXRoIGd1cF9mYXN0LCBkdWUgdG8KPj4gZHluYW1pYyBwYWdlIHRhYmxlIGZvbGRpbmcu 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