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[2003:cb:c701:700:2393:b0f4:ef08:bd51]) by smtp.gmail.com with ESMTPSA id r12-20020a5d694c000000b0020c5253d8c3sm2174483wrw.15.2022.05.11.10.27.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 May 2022 10:27:55 -0700 (PDT) Message-ID: <55e85b3e-dd6a-1dc2-719d-c6be9d5124c0@redhat.com> Date: Wed, 11 May 2022 19:27:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v4 2/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue when migration Content-Language: en-US To: Baolin Wang , akpm@linux-foundation.org, mike.kravetz@oracle.com Cc: catalin.marinas@arm.com, will@kernel.org, songmuchun@bytedance.com, tsbogend@alpha.franken.de, James.Bottomley@HansenPartnership.com, deller@gmx.de, mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, ysato@users.sourceforge.jp, dalias@libc.org, davem@davemloft.net, arnd@arndb.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org References: From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 11.05.22 14:04, Baolin Wang wrote: > On some architectures (like ARM64), it can support CONT-PTE/PMD size > hugetlb, which means it can support not only PMD/PUD size hugetlb: > 2M and 1G, but also CONT-PTE/PMD size: 64K and 32M if a 4K page > size specified. > > When migrating a hugetlb page, we will get the relevant page table > entry by huge_pte_offset() only once to nuke it and remap it with > a migration pte entry. This is correct for PMD or PUD size hugetlb, > since they always contain only one pmd entry or pud entry in the > page table. > > However this is incorrect for CONT-PTE and CONT-PMD size hugetlb, > since they can contain several continuous pte or pmd entry with > same page table attributes. So we will nuke or remap only one pte > or pmd entry for this CONT-PTE/PMD size hugetlb page, which is > not expected for hugetlb migration. The problem is we can still > continue to modify the subpages' data of a hugetlb page during > migrating a hugetlb page, which can cause a serious data consistent > issue, since we did not nuke the page table entry and set a > migration pte for the subpages of a hugetlb page. > > To fix this issue, we should change to use huge_ptep_clear_flush() > to nuke a hugetlb page table, and remap it with set_huge_pte_at() > and set_huge_swap_pte_at() when migrating a hugetlb page, which > already considered the CONT-PTE or CONT-PMD size hugetlb. > > Signed-off-by: Baolin Wang > Reviewed-by: Muchun Song > Reviewed-by: Mike Kravetz Makes sense to me. Acked-by: David Hildenbrand -- Thanks, David / dhildenb