From nobody Sat Dec 27 15:11:26 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 44B11F9E8 for ; Tue, 19 Dec 2023 07:58:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OTbHzUOh" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1702972702; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=z9BJA067XqZpd3Nf7GBMDnnzZoziQMnRZVuO9/Z3c+Q=; b=OTbHzUOhD4SSDuCOhNfkUyCQ8I22WiCN9HszJvBQZiO2UTcyp1bji6bC0rr0/nUv/OVOjb T26ATUEOh0iCI0SC5IKmNUOQgU8ynCbdWm/z7Jmr93+qefu3fNRZLB4PvDMX7Mj3pNU6/C O479d6k+PFO20begR3/oXMxM4G3vG9w= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-175-dRyYBC1tOkeHiKu36YFQHw-1; Tue, 19 Dec 2023 02:58:18 -0500 X-MC-Unique: dRyYBC1tOkeHiKu36YFQHw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7D4B63806720; Tue, 19 Dec 2023 07:58:16 +0000 (UTC) Received: from x1n.redhat.com (unknown [10.72.116.117]) by smtp.corp.redhat.com (Postfix) with ESMTP id 528C52026D66; Tue, 19 Dec 2023 07:58:04 +0000 (UTC) From: peterx@redhat.com To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Matthew Wilcox , Christophe Leroy , Lorenzo Stoakes , David Hildenbrand , Vlastimil Babka , Mike Kravetz , Mike Rapoport , Christoph Hellwig , John Hubbard , Andrew Jones , linux-arm-kernel@lists.infradead.org, Michael Ellerman , "Kirill A . Shutemov" , linuxppc-dev@lists.ozlabs.org, Rik van Riel , linux-riscv@lists.infradead.org, Yang Shi , James Houghton , "Aneesh Kumar K . V" , Andrew Morton , Jason Gunthorpe , Andrea Arcangeli , peterx@redhat.com, Axel Rasmussen Subject: [PATCH 12/13] mm/gup: Handle hugepd for follow_page() Date: Tue, 19 Dec 2023 15:55:37 +0800 Message-ID: <20231219075538.414708-13-peterx@redhat.com> In-Reply-To: <20231219075538.414708-1-peterx@redhat.com> References: <20231219075538.414708-1-peterx@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 Content-Type: text/plain; charset="utf-8" From: Peter Xu Hugepd is only used in PowerPC so far on 4K page size kernels where hash mmu is used. follow_page_mask() used to leverage hugetlb APIs to access hugepd entries. Teach follow_page_mask() itself on hugepd. With previous refactors on fast-gup gup_huge_pd(), most of the code can be easily leveraged. There's something not needed for follow page, for example, gup_hugepte() tries to detect pgtable entry change which will never happen with slow gup (which has the pgtable lock held), but that's not a problem to check. Since follow_page() always only fetch one page, set the end to "address + PAGE_SIZE" should suffice. We will still do the pgtable walk once for each hugetlb page by setting ctx->page_mask properly. One thing worth mentioning is that some level of pgtable's _bad() helper will report is_hugepd() entries as TRUE on Power8 hash MMUs. I think it at least applies to PUD on Power8 with 4K pgsize. It means feeding a hugepd entry to pud_bad() will report a false positive. Let's leave that for now because it can be arch-specific where I am a bit declined to touch. In this patch it's not a problem as long as hugepd is detected before any bad pgtable entries. Signed-off-by: Peter Xu --- mm/gup.c | 78 +++++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 69 insertions(+), 9 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 080dff79b650..14a7d13e7bd6 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -30,6 +30,11 @@ struct follow_page_context { unsigned int page_mask; }; =20 +static struct page *follow_hugepd(struct vm_area_struct *vma, hugepd_t hug= epd, + unsigned long addr, unsigned int pdshift, + unsigned int flags, + struct follow_page_context *ctx); + static inline void sanity_check_pinned_pages(struct page **pages, unsigned long npages) { @@ -871,6 +876,9 @@ static struct page *follow_pmd_mask(struct vm_area_stru= ct *vma, return no_page_table(vma, flags, address); if (!pmd_present(pmdval)) return no_page_table(vma, flags, address); + if (unlikely(is_hugepd(__hugepd(pmd_val(pmdval))))) + return follow_hugepd(vma, __hugepd(pmd_val(pmdval)), + address, PMD_SHIFT, flags, ctx); if (pmd_devmap(pmdval)) { ptl =3D pmd_lock(mm, pmd); page =3D follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap); @@ -921,6 +929,9 @@ static struct page *follow_pud_mask(struct vm_area_stru= ct *vma, pud =3D *pudp; if (pud_none(pud) || !pud_present(pud)) return no_page_table(vma, flags, address); + if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) + return follow_hugepd(vma, __hugepd(pud_val(pud)), + address, PUD_SHIFT, flags, ctx); if (pud_huge(pud)) { ptl =3D pud_lock(mm, pudp); page =3D follow_huge_pud(vma, address, pudp, flags, ctx); @@ -940,13 +951,17 @@ static struct page *follow_p4d_mask(struct vm_area_st= ruct *vma, unsigned int flags, struct follow_page_context *ctx) { - p4d_t *p4d; + p4d_t *p4d, p4dval; =20 p4d =3D p4d_offset(pgdp, address); - if (p4d_none(*p4d)) - return no_page_table(vma, flags, address); - BUILD_BUG_ON(p4d_huge(*p4d)); - if (unlikely(p4d_bad(*p4d))) + p4dval =3D *p4d; + BUILD_BUG_ON(p4d_huge(p4dval)); + + if (unlikely(is_hugepd(__hugepd(p4d_val(p4dval))))) + return follow_hugepd(vma, __hugepd(p4d_val(p4dval)), + address, P4D_SHIFT, flags, ctx); + + if (p4d_none(p4dval) || unlikely(p4d_bad(p4dval))) return no_page_table(vma, flags, address); =20 return follow_pud_mask(vma, address, p4d, flags, ctx); @@ -980,7 +995,7 @@ static struct page *follow_page_mask(struct vm_area_str= uct *vma, unsigned long address, unsigned int flags, struct follow_page_context *ctx) { - pgd_t *pgd; + pgd_t *pgd, pgdval; struct mm_struct *mm =3D vma->vm_mm; =20 ctx->page_mask =3D 0; @@ -995,11 +1010,17 @@ static struct page *follow_page_mask(struct vm_area_= struct *vma, &ctx->page_mask); =20 pgd =3D pgd_offset(mm, address); + pgdval =3D *pgd; =20 - if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) - return no_page_table(vma, flags, address); + if (unlikely(is_hugepd(__hugepd(pgd_val(pgdval))))) + page =3D follow_hugepd(vma, __hugepd(pgd_val(pgdval)), + address, PGDIR_SHIFT, flags, ctx); + else if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) + page =3D no_page_table(vma, flags, address); + else + page =3D follow_p4d_mask(vma, address, pgd, flags, ctx); =20 - return follow_p4d_mask(vma, address, pgd, flags, ctx); + return page; } =20 struct page *follow_page(struct vm_area_struct *vma, unsigned long address, @@ -3026,6 +3047,37 @@ static int gup_huge_pd(hugepd_t hugepd, unsigned lon= g addr, =20 return 1; } + +static struct page *follow_hugepd(struct vm_area_struct *vma, hugepd_t hug= epd, + unsigned long addr, unsigned int pdshift, + unsigned int flags, + struct follow_page_context *ctx) +{ + struct page *page; + struct hstate *h; + spinlock_t *ptl; + int nr =3D 0, ret; + pte_t *ptep; + + /* Only hugetlb supports hugepd */ + if (WARN_ON_ONCE(!is_vm_hugetlb_page(vma))) + return ERR_PTR(-EFAULT); + + h =3D hstate_vma(vma); + ptep =3D hugepte_offset(hugepd, addr, pdshift); + ptl =3D huge_pte_lock(h, vma->vm_mm, ptep); + ret =3D gup_huge_pd(hugepd, addr, pdshift, addr + PAGE_SIZE, + flags, &page, &nr); + spin_unlock(ptl); + + if (ret) { + WARN_ON_ONCE(nr !=3D 1); + ctx->page_mask =3D (1U << huge_page_order(h)) - 1; + return page; + } + + return NULL; +} #else static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr, unsigned int pdshift, unsigned long end, unsigned int flags, @@ -3033,6 +3085,14 @@ static inline int gup_huge_pd(hugepd_t hugepd, unsig= ned long addr, { return 0; } + +static struct page *follow_hugepd(struct vm_area_struct *vma, hugepd_t hug= epd, + unsigned long addr, unsigned int pdshift, + unsigned int flags, + struct follow_page_context *ctx) +{ + return NULL; +} #endif /* CONFIG_ARCH_HAS_HUGEPD */ =20 static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, --=20 2.41.0