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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=GKw/OT+lB3l1dxnftq78lgBEvVmARysDg5OtSIt8bA/Y9aR6w/u75xbPN5yHturYr 6uE2bQOCHNtux/y8TLzNVtju+DviYQLPnEeSd7/zU3dfVFwhUo5bvgCjHLB3wock9U vD6SzIyJGPcTiyXjSqM3Os0+dubnsvnyTrPPtAdU= Message-ID: <45ad2925-9d01-427a-9ac0-650c4b2d07e4@arm.com> Date: Tue, 12 May 2026 11:29:00 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/9] mm/memory: Batch set uffd-wp markers during zapping To: "David Hildenbrand (Arm)" , akpm@linux-foundation.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260506094504.2588857-1-dev.jain@arm.com> <20260506094504.2588857-5-dev.jain@arm.com> <4b36ddb9-c11a-4320-85d4-3e059e67384f@kernel.org> Content-Language: en-US From: Dev Jain In-Reply-To: <4b36ddb9-c11a-4320-85d4-3e059e67384f@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: CDC111A0002 X-Stat-Signature: 3apre47krun7busi85n5ffa76m7k9iap X-HE-Tag: 1778565553-584419 X-HE-Meta: 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 yX8RbGiY WpumiB7w9ZSq6buTETLjqo+WIDprsZkou6ejAMk3e3kFEXzmwGJP7GfUSyJD8AxqDGuGUEv01OUQj5Ysks6npuJuRRRWGaAxkLJF7qK8E63EcIGY+J2ps543YQ4136h2dY/0bRcdh/LyVyXmBNT0lpjE/t3aXvMV0r99IiszqWGn1RTfNEc2WnJ4XKpdr+VzmblbY1OFLJQVvNQWyyJ68GOtwyYlOYku7j1ojWv70W6VToEa2kuEB/Rl1vVV1uvrpUS0P31JJIfnLHx1mgurwGq2PbgVm7IXNAYeR Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/05/26 1:07 pm, David Hildenbrand (Arm) wrote: > On 5/6/26 11:44, Dev Jain wrote: >> In preparation for the next patch, enable batch setting of uffd-wp ptes. >> >> The code paths passing nr > 1 to zap_install_uffd_wp_if_needed() produce >> that nr through either folio_pte_batch or swap_pte_batch, guaranteeing that >> all ptes are the same w.r.t belonging to the same type of VMA (anonymous >> or non-anonymous, wp-armed or non-wp-armed), and all being marked with >> uffd-wp or all being not marked. >> >> Note that we will have to use set_pte_at() in a loop instead of set_ptes() >> since the latter cannot handle present->non-present conversion for >> nr_pages > 1. >> >> Convert documentation of install_uffd_wp_ptes_if_needed to kerneldoc >> format. > > You should mention why the uffd_supports_wp_marker()+vma_is_anonymous() calls in > zap_install_uffd_wp_if_needed can be dropped. Okay. > >> >> No functional change is intended. >> >> Signed-off-by: Dev Jain >> --- >> include/linux/mm_inline.h | 34 +++++++++++++++++++++------------- >> mm/memory.c | 20 +------------------- >> mm/rmap.c | 2 +- >> 3 files changed, 23 insertions(+), 33 deletions(-) >> >> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h >> index a171070e15f05..6f7ecede2fb45 100644 >> --- a/include/linux/mm_inline.h >> +++ b/include/linux/mm_inline.h >> @@ -566,9 +566,17 @@ static inline pte_marker copy_pte_marker( >> return dstm; >> } >> >> -/* >> - * If this pte is wr-protected by uffd-wp in any form, arm the special pte to >> - * replace a none pte. NOTE! This should only be called when *pte is already >> +/** >> + * install_uffd_wp_ptes_if_needed - install uffd-wp marker on PTEs that map >> + * consecutive pages of the same large folio. >> + * @vma: The VMA the pages are mapped into. >> + * @addr: Address the first page of this batch is mapped at. >> + * @ptep: Page table pointer for the first entry of this batch. >> + * @pteval: old value of the entry pointed to by ptep. >> + * @nr_ptes: Number of entries to clear (batch size). >> + * >> + * If the ptes were wr-protected by uffd-wp in any form, arm special ptes to >> + * replace none ptes. NOTE! This should only be called when *pte is already >> * cleared so we will never accidentally replace something valuable. Meanwhile >> * none pte also means we are not demoting the pte so tlb flushed is not needed. >> * E.g., when pte cleared the caller should have taken care of the tlb flush. >> @@ -576,11 +584,11 @@ static inline pte_marker copy_pte_marker( >> * Must be called with pgtable lock held so that no thread will see the none >> * pte, and if they see it, they'll fault and serialize at the pgtable lock. >> * >> - * Returns true if an uffd-wp pte was installed, false otherwise. >> + * Returns true if uffd-wp ptes were installed, false otherwise. >> */ >> static inline bool >> -pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr, >> - pte_t *pte, pte_t pteval) >> +install_uffd_wp_ptes_if_needed(struct vm_area_struct *vma, unsigned long addr, >> + pte_t *ptep, pte_t pteval, unsigned long nr_ptes) > > If we conditionally do something, what about while at it shorten it to: > > cont_install_uffd_wp_ptes() Why "cont_"? Did you mean to say "cond" ("conditionally"). > > Also, less churn in this patch if you don't change pte->ptep > > (because if you do, you should then also do pteval->pte :) ) > > So I'd just leave that as is in this patch. So I'll change pte->ptep and pteval->pte because I hate pte pointers called pte : ) > >> { >> bool arm_uffd_pte = false; >> >> @@ -588,7 +596,7 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr, >> return false; >> >> /* The current status of the pte should be "cleared" before calling */ >> - WARN_ON_ONCE(!pte_none(ptep_get(pte))); >> + WARN_ON_ONCE(!pte_none(ptep_get(ptep))); >> >> /* >> * NOTE: userfaultfd_wp_unpopulated() doesn't need this whole >> @@ -610,13 +618,13 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr, >> if (unlikely(pte_swp_uffd_wp_any(pteval))) >> arm_uffd_pte = true; >> >> - if (unlikely(arm_uffd_pte)) { >> - set_pte_at(vma->vm_mm, addr, pte, >> - make_pte_marker(PTE_MARKER_UFFD_WP)); >> - return true; >> - } >> + if (likely(!arm_uffd_pte)) >> + return false; >> >> - return false; >> + for (int i = 0; i < nr_ptes; ++i, ++ptep, addr += PAGE_SIZE) >> + set_pte_at(vma->vm_mm, addr, ptep, make_pte_marker(PTE_MARKER_UFFD_WP)); >> + >> + return true; >> } > > I wonder whether this growing function is really appropriate to be in the header > file? Can we just move that whole thing into mm/memory.c? > > It's called on every try_to_unmap_one() invocation, but I doubt we care about a > function call here. Makes sense. > >> >> static inline bool vma_has_recency(const struct vm_area_struct *vma) >> diff --git a/mm/memory.c b/mm/memory.c >> index 0c9d9c2cbf0e0..f14311c4d2001 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -1610,29 +1610,11 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma, >> unsigned long addr, pte_t *pte, int nr, >> struct zap_details *details, pte_t pteval) >> { >> - bool was_installed = false; >> - >> - if (!uffd_supports_wp_marker()) >> - return false; >> - >> - /* Zap on anonymous always means dropping everything */ >> - if (vma_is_anonymous(vma)) >> - return false; >> - >> if (zap_drop_markers(details)) >> return false; >> >> - for (;;) { >> - /* the PFN in the PTE is irrelevant. */ >> - if (pte_install_uffd_wp_if_needed(vma, addr, pte, pteval)) >> - was_installed = true; >> - if (--nr == 0) >> - break; >> - pte++; >> - addr += PAGE_SIZE; >> - } >> + return install_uffd_wp_ptes_if_needed(vma, addr, pte, pteval, nr); >> >> - return was_installed; >> } >> >> static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb, >> diff --git a/mm/rmap.c b/mm/rmap.c >> index bd4e3639e26ed..b17dce752a1ea 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -2266,7 +2266,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> * we may want to replace a none pte with a marker pte if >> * it's file-backed, so we don't lose the tracking info. >> */ >> - pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval); >> + install_uffd_wp_ptes_if_needed(vma, address, pvmw.pte, pteval, 1); >> >> /* Update high watermark before we lower rss */ >> update_hiwater_rss(mm); > >