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[85.23.48.202]) by smtp.gmail.com with ESMTPSA id v7-20020a2e87c7000000b002a2b9d9429esm832740ljj.117.2023.04.14.07.23.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Apr 2023 07:23:21 -0700 (PDT) Message-ID: Date: Fri, 14 Apr 2023 17:23:12 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH 1/6] mm/hugetlb: Fix uffd-wp during fork() Content-Language: en-US To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Axel Rasmussen , Andrew Morton , David Hildenbrand , Mike Kravetz , Nadav Amit , Andrea Arcangeli , linux-stable References: <20230413231120.544685-1-peterx@redhat.com> <20230413231120.544685-2-peterx@redhat.com> <9cb84b60-6b51-3117-27cb-a29b3bd9e741@mbosol.com> From: =?UTF-8?Q?Mika_Penttil=c3=a4?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 14.4.2023 17.09, Peter Xu wrote: > On Fri, Apr 14, 2023 at 12:45:29PM +0300, Mika Penttilä wrote: >>> } else if (unlikely(is_hugetlb_entry_migration(entry))) { >>> swp_entry_t swp_entry = pte_to_swp_entry(entry); >>> - bool uffd_wp = huge_pte_uffd_wp(entry); > > [1] > >>> if (!is_readable_migration_entry(swp_entry) && cow) { >>> /* >>> @@ -5049,11 +5050,12 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, >>> swp_entry = make_readable_migration_entry( >>> swp_offset(swp_entry)); >>> entry = swp_entry_to_pte(swp_entry); > > [2] > >>> - if (userfaultfd_wp(src_vma) && uffd_wp) >>> - entry = huge_pte_mkuffd_wp(entry); >>> + if (userfaultfd_wp(src_vma) && >>> + pte_swp_uffd_wp(entry)) >>> + entry = pte_swp_mkuffd_wp(entry); >> >> >> This looks interesting with pte_swp_uffd_wp and pte_swp_mkuffd_wp ? > > Could you explain what do you mean? > Yes like you noticed also you called pte_swp_mkuffd_wp(entry) iff pte_swp_uffd_wp(entry) which is of course a nop. But the fixup not dropping the temp var should work. > I think these helpers are the right ones to use, as afaict hugetlb > migration should follow the same pte format with !hugetlb. However, I > noticed I did it wrong when dropping the temp var - when at [1], "entry" > still points to the src entry, but at [2] it's already pointing to the > newly created one.. so I think I can't drop the var, a fixup should like: > > ===8<=== > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 083aae35bff8..cd3a9d8f4b70 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5041,6 +5041,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, > set_huge_pte_at(dst, addr, dst_pte, entry); > } else if (unlikely(is_hugetlb_entry_migration(entry))) { > swp_entry_t swp_entry = pte_to_swp_entry(entry); > + bool uffd_wp = pte_swp_uffd_wp(entry); > > if (!is_readable_migration_entry(swp_entry) && cow) { > /* > @@ -5050,8 +5051,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, > swp_entry = make_readable_migration_entry( > swp_offset(swp_entry)); > entry = swp_entry_to_pte(swp_entry); > - if (userfaultfd_wp(src_vma) && > - pte_swp_uffd_wp(entry)) > + if (userfaultfd_wp(src_vma) && uffd_wp) > entry = pte_swp_mkuffd_wp(entry); > set_huge_pte_at(src, addr, src_pte, entry); > ===8<=== > > Besides, did I miss something else? > > Thanks, > --Mika