From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f69.google.com (mail-pj1-f69.google.com [209.85.216.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C1A8223E33D for ; Sat, 3 Oct 2026 00:21:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.69 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790986917; cv=none; b=iHOFw3lKrYmFbo2EIu880TOYQGlQixith2a/A5t+Z80DI2haMKF1AM64wFsCpOQBJ+oLcoMb/GJxVuef4LosD8NBe8o3NHfHg4WiO2o+sW2n8t2lKPWZGJ3X8u/AV3vvvLw0m9eAKkVMAVYHTwAkdCngMniiyJlooiIRAL7r4sM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790986917; c=relaxed/simple; bh=6DbAoncHxnK0azOb1VY6m/Px0Gjjk+3ADgI/O3v3Y9Y=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=VYGt1ndZzkPLE81HC0LBX6WmcsybSmTm9SCblkwoA5i1z2ee6FMSNWx4JhRoi676o7OEOVX2RgwwCwOjZcdbto73wD0AKcl200eyeHI+A9oKhmxy/7xSPNAli2sIMK2H3oJV817bZAH0Rv+9nV7pHL7xP7pC39OsDK59XILVMB0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jthoughton.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=aczeoNAJ; arc=none smtp.client-ip=209.85.216.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jthoughton.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="aczeoNAJ" Received: by mail-pj1-f69.google.com with SMTP id 98e67ed59e1d1-38e8e864ef0so3572a91.0 for ; Fri, 02 Oct 2026 17:21:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1790986910; x=1791591710; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=tCgjHn2mz/yCHbbXpM7X3kmHNH/eC22IJjKzJWGDoHY=; b=aczeoNAJRY2bSFAdJKDS+WaVtzinEqUKNI2ZdR1R1cvfCbNr+WiDUaMWHkHRsVrzPQ fYPylbj6Qpq5NpjI5mPPwQnJ18Mp+lW4CQCbo8kMyGLE55X7vNoc7V0gx9FSF16WTeMg AKhfBt/VutFZvUOFs9fzuIq5Hoh7pzPXqHLf7jpMVcQnEJvQoIpqAFqXefegVeezdoMT yNcIIaKbaWUfLhnAZN6xg8l6fvBO/JoLOTITla11e/RdKWQinlQ0TlRCX7nxqTph6ccf reX+xz0LU0P6FEY1MYDfUQPtMJvn//O57yG6YwjvYuNJ8l49zlK1mWBRqYonsx7KAPXX UH9g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790986910; x=1791591710; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=tCgjHn2mz/yCHbbXpM7X3kmHNH/eC22IJjKzJWGDoHY=; b=vIQ4G39Dd4ABomFOHVbxd30K6vWl296Qq0FY+h18urlLprra2qZmJWtQA2CE9KauRY LZGXy6raCj9c3/YM4VqPdyjm+uMTPLpiDgRSUvqbqm7ZWiUNsyl2fzE8j1MAoMvmFGJ6 D4qurT7u6sGxcyhYGSFtExZCw2owFuURqzJNYcw4ROqC+IB1SgK4FjUBzABarhL6hgdk 8RH79scET5C+5TnLQwBlKLHyyy4hr4RPD/FB6OJcPvs+6M+KglIny9xnTfxUt8jLWh1l 8UxvbT6LZfwDlmRN11AuifbcGxWqxF/pYocw7WDQtkxDDaBmqWux4QG6K8i5L46AsE5u EBxA== X-Forwarded-Encrypted: i=1; AKwUvBx6odbD7wOZBAayujMfG3t4I3dX/6AEZUGYm4qHAPQgIabOTpQfu1tueo9D7IfW+8rz1dgAJBuEOpvogkE=@vger.kernel.org X-Gm-Message-State: AFq9FYKAhKCJH1EMyFlVxjhFKDVavQUp7ME3KhtEg3dzG18k7t7RKf9r 7vZLqZOgqy5Tszee+N7IDLIt0Uhk+bL/zBFmLVpgeto2AFXxtux4ymXyQp8VqjIw6A3M5RAGA/s yyf7Gcg8PWwa2ZSSgqUEGmg== X-Received: from pjbmv17.prod.google.com ([2002:a17:90b:1991:b0:3a6:f87a:f3e4]) (user=jthoughton job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:33cc:b0:3a2:bb45:d37b with SMTP id 98e67ed59e1d1-3a6ceb00093mr2158482a91.25.1790986909781; Fri, 02 Oct 2026 17:21:49 -0700 (PDT) Date: Sat, 3 Oct 2026 00:21:20 +0000 In-Reply-To: <20261003002123.505555-1-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20261003002123.505555-1-jthoughton@google.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Message-ID: <20261003002123.505555-18-jthoughton@google.com> Subject: [PATCH v2 17/20 DO-NOT-MERGE] arm64: Implement try_populate_vmemmap_pmd using AF trick From: James Houghton To: Will Deacon , Catalin Marinas , Muchun Song , Oscar Salvador , Andrew Morton Cc: Nikos Nikoleris , Linu Cherian , Mark Rutland , David Hildenbrand , Ryan Roberts , Nanyong Sun , Yu Zhao , Frank van der Linden , David Rientjes , James Houghton , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" This routine is to be used for updating in-use, leaf-level PMDs in the vmemmap without introducing a window where vmemmap accesses might fault. Implementing this on arm64 requires some care: use the same access flag trick that is used for vmemmap PTE updates. HAFT is not needed and the TLB flushing routine remains identical, as we are not overwriting a non-leaf PMD. For systems that support BBML3, there is no need to use the AF trick. Signed-off-by: James Houghton --- This patch is the main questionable piece of this "DO-NOT-MERGE" part of the series. It's unclear if the Arm ARM truly requires hardware implementations not to cache anything about AF=0 Block translations. --- arch/arm64/include/asm/pgalloc.h | 51 ++++++++++++++++++++++++++++++-- 1 file changed, 48 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h index 0263329fb7b3..7e304f01ce6d 100644 --- a/arch/arm64/include/asm/pgalloc.h +++ b/arch/arm64/include/asm/pgalloc.h @@ -124,9 +124,54 @@ pmd_populate(struct mm_struct *mm, pmd_t *pmdp, pgtable_t ptep) static inline int try_populate_vmemmap_pmd(unsigned long addr, pmd_t *pmdp, pte_t *pgtable) { - /* BBLM3 is required. Its presence has been checked. */ - pmd_populate_kernel(&init_mm, pmdp, pgtable); - return 0; + const int max_attempts = 16; + int attempts = 0; + pmd_t old_pmd, new_pmd; + + if (!system_supports_bbm_through_af()) + return -EOPNOTSUPP; + + if (system_supports_bbml3()) { + /* + * BBML3 allows block->table transitions if the PTEs underneath + * do not conflict with existing, potentially cached + * translations. + */ + pmd_populate_kernel(&init_mm, pmdp, pgtable); + return 0; + } + + new_pmd = __pmd(__phys_to_pmd_val(__pa(pgtable)) | + PMD_TYPE_TABLE | PMD_TABLE_AF | PMD_TABLE_UXN); + + old_pmd = pmdp_get(pmdp); + + do { + if (WARN_ON_ONCE(!pmd_valid(old_pmd))) + return -EINVAL; + + if (WARN_ON_ONCE(!pmd_leaf(old_pmd))) + return -EINVAL; + + /* We should never get a contiguous PMD here. */ + if (WARN_ON_ONCE(pmd_cont(old_pmd))) + return -EINVAL; + + if (pmd_young(old_pmd)) { + /* __ptep_clear_young() returns the overwritten PTE */ + old_pmd = pte_pmd(pte_mkold(__ptep_clear_young((pte_t *)pmdp))); + + flush_tlb_kernel_range(addr, addr + PMD_SIZE); + } + /* + * Translations without AF cannot be cached, so we can replace + * them without BBM. + */ + } while (!try_cmpxchg_relaxed(&pmd_val(*pmdp), &pmd_val(old_pmd), + pmd_val(new_pmd)) && + ++attempts < max_attempts); + + return attempts == max_attempts ? -EAGAIN : 0; } #endif -- 2.56.0.rc1.315.gc6ed9934b7-goog