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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id f24-20020ac84658000000b003b9a73cd120sm4059709qto.17.2023.04.05.08.43.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Apr 2023 08:43:21 -0700 (PDT) Date: Wed, 5 Apr 2023 11:43:19 -0400 From: Peter Xu To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Muhammad Usama Anjum , stable@vger.kernel.org Subject: Re: [PATCH v1 1/2] mm/userfaultfd: fix uffd-wp handling for THP migration entries Message-ID: References: <20230405142535.493854-1-david@redhat.com> <20230405142535.493854-2-david@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: E36C140017 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: zufdt1j5w5w8rukgf3m1udbo9g8e767f X-HE-Tag: 1680709405-916026 X-HE-Meta: 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 LLeV+aBP CEzDQMgHSWb2XDmCLFWW2vobeeOFFBAEZaoc1aduyDueLv7WxBLgt8OvGi09VVelXG8iR0T1/C1sBl+REWz82Ryvyp6sdy7oJt2IQ5GygOn5R8Z+hAiSF73US6pLMDbszk2wDHzU2f4YCMHDUFCWmEVyN1T/5nLEj9jtoOv25mRSFL61CaNGPL02dgLKOIHTq8oMkkgDwhL6gMCkNg6be40n9umQCsdv3m+sWOUfTh1stTOZilre+G7IrqzuiXal3233cKGAyKF5v/smcfN57wVGpS3y+jx9b4ZR5yS8Ulb7Qq3DVDipCh/8wxsWx/jLc+XBfNho/ghsI4bcaQZFxkjNnN7F6i2AHiyLyBfHCqK9xQ2BDbcdEeKkfVJU4nYAR9PhpfN3SZlt9LTvcxCPV15SHlDpPlesTGwhlhb7uisOyI+M06If8IgmgLaIO9Vncw7TQfMoEPiEyTlQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Apr 05, 2023 at 05:17:31PM +0200, David Hildenbrand wrote: > On 05.04.23 17:12, Peter Xu wrote: > > On Wed, Apr 05, 2023 at 04:25:34PM +0200, David Hildenbrand wrote: > > > Looks like what we fixed for hugetlb in commit 44f86392bdd1 ("mm/hugetlb: > > > fix uffd-wp handling for migration entries in hugetlb_change_protection()") > > > similarly applies to THP. > > > > > > Setting/clearing uffd-wp on THP migration entries is not implemented > > > properly. Further, while removing migration PMDs considers the uffd-wp > > > bit, inserting migration PMDs does not consider the uffd-wp bit. > > > > > > We have to set/clear independently of the migration entry type in > > > change_huge_pmd() and properly copy the uffd-wp bit in > > > set_pmd_migration_entry(). > > > > > > Verified using a simple reproducer that triggers migration of a THP, that > > > the set_pmd_migration_entry() no longer loses the uffd-wp bit. > > > > > > Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: David Hildenbrand > > > > Reviewed-by: Peter Xu > > > > Thanks, one trivial nitpick: > > > > > --- > > > mm/huge_memory.c | 14 ++++++++++++-- > > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > index 032fb0ef9cd1..bdda4f426d58 100644 > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > @@ -1838,10 +1838,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > > > if (is_swap_pmd(*pmd)) { > > > swp_entry_t entry = pmd_to_swp_entry(*pmd); > > > struct page *page = pfn_swap_entry_to_page(entry); > > > + pmd_t newpmd; > > > VM_BUG_ON(!is_pmd_migration_entry(*pmd)); > > > if (is_writable_migration_entry(entry)) { > > > - pmd_t newpmd; > > > /* > > > * A protection check is difficult so > > > * just be safe and disable write > > > @@ -1855,8 +1855,16 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > > > newpmd = pmd_swp_mksoft_dirty(newpmd); > > > if (pmd_swp_uffd_wp(*pmd)) > > > newpmd = pmd_swp_mkuffd_wp(newpmd); > > > - set_pmd_at(mm, addr, pmd, newpmd); > > > + } else { > > > + newpmd = *pmd; > > > } > > > + > > > + if (uffd_wp) > > > + newpmd = pmd_swp_mkuffd_wp(newpmd); > > > + else if (uffd_wp_resolve) > > > + newpmd = pmd_swp_clear_uffd_wp(newpmd); > > > + if (!pmd_same(*pmd, newpmd)) > > > + set_pmd_at(mm, addr, pmd, newpmd); > > > goto unlock; > > > } > > > #endif > > > @@ -3251,6 +3259,8 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, > > > pmdswp = swp_entry_to_pmd(entry); > > > if (pmd_soft_dirty(pmdval)) > > > pmdswp = pmd_swp_mksoft_dirty(pmdswp); > > > + if (pmd_swp_uffd_wp(*pvmw->pmd)) > > > + pmdswp = pmd_swp_mkuffd_wp(pmdswp); > > > > I think it's fine to use *pmd, but maybe still better to use pmdval? I > > worry pmdp_invalidate()) can be something else in the future that may > > affect the bit. > > Wondering how I ended up with that, I realized that it's actually > wrong and might have worked by chance for my reproducer on x86. > > That should make it work: > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index f977c965fdad..fffc953fa6ea 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3257,7 +3257,7 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, > pmdswp = swp_entry_to_pmd(entry); > if (pmd_soft_dirty(pmdval)) > pmdswp = pmd_swp_mksoft_dirty(pmdswp); > - if (pmd_swp_uffd_wp(*pvmw->pmd)) > + if (pmd_uffd_wp(pmdval)) > pmdswp = pmd_swp_mkuffd_wp(pmdswp); > set_pmd_at(mm, address, pvmw->pmd, pmdswp); > page_remove_rmap(page, vma, true); I guess pmd_swp_uffd_wp() just reads the _USER bit 2 which is also set for a present pte, but then it sets swp uffd-wp always even if it was not set. Yes the change must be squashed in to be correct, with that, my R-b keeps. Thanks, -- Peter Xu