From nobody Sun Feb 8 20:29:05 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C71BC77B7A for ; Mon, 29 May 2023 18:00:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229528AbjE2SAd (ORCPT ); Mon, 29 May 2023 14:00:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36144 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229453AbjE2SAb (ORCPT ); Mon, 29 May 2023 14:00:31 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 344CED2 for ; Mon, 29 May 2023 11:00:30 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B2ED3616FE for ; Mon, 29 May 2023 18:00:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 27062C433D2; Mon, 29 May 2023 18:00:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1685383229; bh=gJZ6i/YEnspBK6Kp4eZbVclre0eMmwrGGq06qCquzoU=; h=From:To:Cc:Subject:Date:From; b=dBaihDRVF/Dkad7v2ZgMsCQOwVB60RQvPXfXbZJE+4jLWCmYwYMZcv+IeFgKN4nlI qjlIdU/+f49JykEQI5cJEXzvPatnSWW+R4SeQ0sj3iS02QPXHC7w1g07/6d2HtOkJl zDvtwWdeh/gtkzTkkTk9xJSMWQZ9r0miuCMfr4a9dC7X+MNlaluy1HwR7tQGzKvNe7 JkhhyprDfm8iN+Y8eZHAO0juHbS6AjSMc5hoCMLRZkMQcY25TBKLZo5QnedSvLwZYg +ub+9Oiy+pr3PncbWYVPCPZ6TgInAbwXUjWscrTK7vHFPs3mRzFZX1zOskVu91TwLg dKSKOonkpEp/w== From: =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= To: Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org Cc: =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux@rivosinc.com, Alexandre Ghiti , Joerg Roedel Subject: [PATCH] riscv: mm: Pre-allocate PGD entries vmalloc/modules area Date: Mon, 29 May 2023 20:00:23 +0200 Message-Id: <20230529180023.289904-1-bjorn@kernel.org> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Bj=C3=B6rn T=C3=B6pel The RISC-V port requires that kernel PGD entries are to be synchronized between MMs. This is done via the vmalloc_fault() function, that simply copies the PGD entries from init_mm to the faulting one. Historically, faulting in PGD entries have been a source for both bugs [1], and poor performance. One way to get rid of vmalloc faults is by pre-allocating the PGD entries. Pre-allocating the entries potientially wastes 64 * 4K (65 on SV39). The pre-allocation function is pulled from J=C3=B6rg R=C3=B6del's x86 work, with the addition of 3-level page tables (PMD allocations). The pmd_alloc() function needs the ptlock cache to be initialized (when split page locks is enabled), so the pre-allocation is done in a RISC-V specific pgtable_cache_init() implementation. Pre-allocate the kernel PGD entries for the vmalloc/modules area, but only for 64b platforms. Link: https://lore.kernel.org/lkml/20200508144043.13893-1-joro@8bytes.org/ = # [1] Signed-off-by: Bj=C3=B6rn T=C3=B6pel Reviewed-by: Palmer Dabbelt --- arch/riscv/mm/fault.c | 20 +++------------ arch/riscv/mm/init.c | 58 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 62 insertions(+), 16 deletions(-) diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c index 8685f85a7474..6b0b5e517e12 100644 --- a/arch/riscv/mm/fault.c +++ b/arch/riscv/mm/fault.c @@ -230,32 +230,20 @@ void handle_page_fault(struct pt_regs *regs) return; =20 /* - * Fault-in kernel-space virtual memory on-demand. - * The 'reference' page table is init_mm.pgd. + * Fault-in kernel-space virtual memory on-demand, for 32-bit + * architectures. The 'reference' page table is init_mm.pgd. * * NOTE! We MUST NOT take any locks for this case. We may * be in an interrupt or a critical region, and should * only copy the information from the master page table, * nothing more. */ - if (unlikely((addr >=3D VMALLOC_START) && (addr < VMALLOC_END))) { + if (!IS_ENABLED(CONFIG_64BIT) && + unlikely(addr >=3D VMALLOC_START && addr < VMALLOC_END)) { vmalloc_fault(regs, code, addr); return; } =20 -#ifdef CONFIG_64BIT - /* - * Modules in 64bit kernels lie in their own virtual region which is not - * in the vmalloc region, but dealing with page faults in this region - * or the vmalloc region amounts to doing the same thing: checking that - * the mapping exists in init_mm.pgd and updating user page table, so - * just use vmalloc_fault. - */ - if (unlikely(addr >=3D MODULES_VADDR && addr < MODULES_END)) { - vmalloc_fault(regs, code, addr); - return; - } -#endif /* Enable interrupts if they were enabled in the parent context. */ if (!regs_irqs_disabled(regs)) local_irq_enable(); diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index 747e5b1ef02d..38bd4dd95276 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -1363,3 +1363,61 @@ int __meminit vmemmap_populate(unsigned long start, = unsigned long end, int node, return vmemmap_populate_basepages(start, end, node, NULL); } #endif + +#ifdef CONFIG_64BIT +/* + * Pre-allocates page-table pages for a specific area in the kernel + * page-table. Only the level which needs to be synchronized between + * all page-tables is allocated because the synchronization can be + * expensive. + */ +static void __init preallocate_pgd_pages_range(unsigned long start, unsign= ed long end, + const char *area) +{ + unsigned long addr; + const char *lvl; + + for (addr =3D start; addr < end && addr >=3D start; addr =3D ALIGN(addr += 1, PGDIR_SIZE)) { + pgd_t *pgd =3D pgd_offset_k(addr); + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + + lvl =3D "p4d"; + p4d =3D p4d_alloc(&init_mm, pgd, addr); + if (!p4d) + goto failed; + + if (pgtable_l5_enabled) + continue; + + lvl =3D "pud"; + pud =3D pud_alloc(&init_mm, p4d, addr); + if (!pud) + goto failed; + + if (pgtable_l4_enabled) + continue; + + lvl =3D "pmd"; + pmd =3D pmd_alloc(&init_mm, pud, addr); + if (!pmd) + goto failed; + } + return; + +failed: + /* + * The pages have to be there now or they will be missing in + * process page-tables later. + */ + panic("Failed to pre-allocate %s pages for %s area\n", lvl, area); +} + +void __init pgtable_cache_init(void) +{ + preallocate_pgd_pages_range(VMALLOC_START, VMALLOC_END, "vmalloc"); + if (IS_ENABLED(CONFIG_MODULES)) + preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules"); +} +#endif base-commit: ac9a78681b921877518763ba0e89202254349d1b --=20 2.39.2