From mboxrd@z Thu Jan 1 00:00:00 1970 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 62E9DEF99FB for ; Tue, 17 Feb 2026 13:34:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=njM0QEUiS6NSuH0DKTWuny9b1XcS0w9x+jxcchTnf7M=; b=ySF/IuQbFcti7qPfhp3uDowWd1 hJ/1TXX6wBU0G0LecaycBkEAL7EDeK5Z6QGuf86cNPSx81sWtJnbA0ElJb+SNY/FQkTNVd6iQ01Ed DeQ4CTI0ai/XLOGwzN5KQ5Pj7dyOa0dXMlTjSdlo+iZ2jM6qaXhcSLh5xCppiXG8R1iIKadtL8K02 6xw3F0VcjICG/bSFqPWVK02scTw0YHfJKy6in8v8v0OTwOd8pgCosE/lnX9Nj0dExSh4s3CaGE082 FoOH1gVGWGxPeFSbWDxTb57Ep2LMmmFODyMErSU+8QYrqmj/ot/w3DctoeqckK4WF1WzfIXeelPTa dMit07QQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vsLDo-00000008KE3-0ucg; Tue, 17 Feb 2026 13:34:36 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vsLDh-00000008KCL-4AcQ for linux-arm-kernel@lists.infradead.org; Tue, 17 Feb 2026 13:34:31 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 74A1815A1; Tue, 17 Feb 2026 05:34:22 -0800 (PST) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.27]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1121A3F632; Tue, 17 Feb 2026 05:34:26 -0800 (PST) From: Ryan Roberts To: stable@vger.kernel.org Cc: Ryan Roberts , catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Jack Aboutboul , Sharath George John , Noah Meyerhans , Jim Perrin , Mark Rutland , Itaru Kitayama , Eric Chanudet , Ard Biesheuvel Subject: [PATCH 6.6 3/3] arm64: mm: Don't remap pgtables for allocate vs populate Date: Tue, 17 Feb 2026 13:34:08 +0000 Message-ID: <20260217133411.2881311-4-ryan.roberts@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260217133411.2881311-1-ryan.roberts@arm.com> References: <20260217133411.2881311-1-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260217_053430_142888_ED52B328 X-CRM114-Status: GOOD ( 16.27 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org [ Upstream commit 0e9df1c905d8293d333ace86c13d147382f5caf9 ] During linear map pgtable creation, each pgtable is fixmapped / fixunmapped twice; once during allocation to zero the memory, and a again during population to write the entries. This means each table has 2 TLB invalidations issued against it. Let's fix this so that each table is only fixmapped/fixunmapped once, halving the number of TLBIs, and improving performance. Achieve this by separating allocation and initialization (zeroing) of the page. The allocated page is now fixmapped directly by the walker and initialized, before being populated and finally fixunmapped. This approach keeps the change small, but has the side effect that late allocations (using __get_free_page()) must also go through the generic memory clearing routine. So let's tell __get_free_page() not to zero the memory to avoid duplication. Additionally this approach means that fixmap/fixunmap is still used for late pgtable modifications. That's not technically needed since the memory is all mapped in the linear map by that point. That's left as a possible future optimization if found to be needed. Execution time of map_mem(), which creates the kernel linear map page tables, was measured on different machines with different RAM configs: | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra | VM, 16G | VM, 64G | VM, 256G | Metal, 512G ---------------|-------------|-------------|-------------|------------- | ms (%) | ms (%) | ms (%) | ms (%) ---------------|-------------|-------------|-------------|------------- before | 11 (0%) | 161 (0%) | 656 (0%) | 1654 (0%) after | 10 (-11%) | 104 (-35%) | 438 (-33%) | 1223 (-26%) Signed-off-by: Ryan Roberts Suggested-by: Mark Rutland Tested-by: Itaru Kitayama Tested-by: Eric Chanudet Reviewed-by: Mark Rutland Reviewed-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20240412131908.433043-4-ryan.roberts@arm.com Signed-off-by: Will Deacon [ Ryan: Trivial backport ] Signed-off-by: Ryan Roberts --- arch/arm64/mm/mmu.c | 58 ++++++++++++++++++++++----------------------- 1 file changed, 29 insertions(+), 29 deletions(-) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index c1dedd0b59f1b..d6411f7f0b72c 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -106,28 +106,12 @@ EXPORT_SYMBOL(phys_mem_access_prot); static phys_addr_t __init early_pgtable_alloc(int shift) { phys_addr_t phys; - void *ptr; phys = memblock_phys_alloc_range(PAGE_SIZE, PAGE_SIZE, 0, MEMBLOCK_ALLOC_NOLEAKTRACE); if (!phys) panic("Failed to allocate page table page\n"); - /* - * The FIX_{PGD,PUD,PMD} slots may be in active use, but the FIX_PTE - * slot will be free, so we can (ab)use the FIX_PTE slot to initialise - * any level of table. - */ - ptr = pte_set_fixmap(phys); - - memset(ptr, 0, PAGE_SIZE); - - /* - * Implicit barriers also ensure the zeroed page is visible to the page - * table walker - */ - pte_clear_fixmap(); - return phys; } @@ -169,6 +153,14 @@ bool pgattr_change_is_safe(u64 old, u64 new) return ((old ^ new) & ~mask) == 0; } +static void init_clear_pgtable(void *table) +{ + clear_page(table); + + /* Ensure the zeroing is observed by page table walks. */ + dsb(ishst); +} + static void init_pte(pte_t *ptep, unsigned long addr, unsigned long end, phys_addr_t phys, pgprot_t prot) { @@ -211,12 +203,15 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, pmdval |= PMD_TABLE_PXN; BUG_ON(!pgtable_alloc); pte_phys = pgtable_alloc(PAGE_SHIFT); + ptep = pte_set_fixmap(pte_phys); + init_clear_pgtable(ptep); + ptep += pte_index(addr); __pmd_populate(pmdp, pte_phys, pmdval); - pmd = READ_ONCE(*pmdp); + } else { + BUG_ON(pmd_bad(pmd)); + ptep = pte_set_fixmap_offset(pmdp, addr); } - BUG_ON(pmd_bad(pmd)); - ptep = pte_set_fixmap_offset(pmdp, addr); do { pgprot_t __prot = prot; @@ -295,12 +290,15 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, pudval |= PUD_TABLE_PXN; BUG_ON(!pgtable_alloc); pmd_phys = pgtable_alloc(PMD_SHIFT); + pmdp = pmd_set_fixmap(pmd_phys); + init_clear_pgtable(pmdp); + pmdp += pmd_index(addr); __pud_populate(pudp, pmd_phys, pudval); - pud = READ_ONCE(*pudp); + } else { + BUG_ON(pud_bad(pud)); + pmdp = pmd_set_fixmap_offset(pudp, addr); } - BUG_ON(pud_bad(pud)); - pmdp = pmd_set_fixmap_offset(pudp, addr); do { pgprot_t __prot = prot; @@ -338,12 +336,15 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, p4dval |= P4D_TABLE_PXN; BUG_ON(!pgtable_alloc); pud_phys = pgtable_alloc(PUD_SHIFT); + pudp = pud_set_fixmap(pud_phys); + init_clear_pgtable(pudp); + pudp += pud_index(addr); __p4d_populate(p4dp, pud_phys, p4dval); - p4d = READ_ONCE(*p4dp); + } else { + BUG_ON(p4d_bad(p4d)); + pudp = pud_set_fixmap_offset(p4dp, addr); } - BUG_ON(p4d_bad(p4d)); - pudp = pud_set_fixmap_offset(p4dp, addr); do { pud_t old_pud = READ_ONCE(*pudp); @@ -425,11 +426,10 @@ void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt, static phys_addr_t __pgd_pgtable_alloc(int shift) { - void *ptr = (void *)__get_free_page(GFP_PGTABLE_KERNEL); - BUG_ON(!ptr); + /* Page is zeroed by init_clear_pgtable() so don't duplicate effort. */ + void *ptr = (void *)__get_free_page(GFP_PGTABLE_KERNEL & ~__GFP_ZERO); - /* Ensure the zeroed page is visible to the page table walker */ - dsb(ishst); + BUG_ON(!ptr); return __pa(ptr); } -- 2.43.0