From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 05E042853F3 for ; Tue, 13 Oct 2026 07:40:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791877202; cv=none; b=vFFxIiNg2pbELsAehPuRXk57uoaMhHOHBjNXYvjdd5yAmYY7/VFV23MBmKwXEDoHDdcH+/sPHb6pCL00LuhWXhvJXNe7usuhN+s96/JKabzqBWDRcL5DHVkpWtuzq8QlZ26/OBRyvHhXEqcsxJWJTgnegGkM1EOp+yXzAsaco6I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791877202; c=relaxed/simple; bh=M8llo/S2WOJYXxGzPQybCxI1sJWUzWAtW3Z0i4gJyeI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aoc8DoABuU4Z6/VwY6PSF4IdaYcQiUSvyz36cKsIGqwpW8DJ0YpCoX2rh2157XRh2SDcn6QDN/aOl9cUiWxFDZE5+qCpIZTYd2CecnRKXCB1BVuTc8xQIJ2MklSz+R7e3uGoq7j4Bby6tbLT+Kx4v0M4Y7tCKoNn21/7J6zX06k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ryr1uyc5; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ryr1uyc5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CC5B61F000FF; Tue, 13 Oct 2026 07:39:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791877201; bh=Ka4WnGpN0d9oCcVY/MuEpnfOHeYeKtz3o+TrxhSWjCo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Ryr1uyc5yP/JYFWgvjsKT+2rhhWZifPokb2ZTKhhSwbk3itoTBEivaDIZj6NndAoR sTy6b2LkupMAxc5rFehpkbjqkfGOIK1+0VJTeO3B0xu7K7Kaktg8vpRlhKRjkMHU+I I4Ph5lYJzyqydt1ULvEPikXSD6eupUTUiKmz3i1klD3tn6GXk8iZe/ojaxL3LxA/UF RsXSRdN+MrTyWzF3a3ZMv1+ZQ+1zrZ1QNxGD/EZ6i9EgKaQ1QsuxnYbq0a+Wxld9jj 25A0ZRbn9O95WUGGaXfMfVrnugdSC0OhVzh5JfrkiN3hXzwT8sAuq6H28N7ASZ2XKi FWO//HPmJavLw== Message-ID: <67c30e4c-3576-4ded-a71f-b49075ed42e3@kernel.org> Date: Tue, 13 Oct 2026 09:39:54 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: fix uffd move-pmd test crash on 64K base page systems To: Zenghui Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com References: <20261011163527.95988-1-zenghui.yu@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/11/26 18:35, Zenghui Yu wrote: > From: "Zenghui Yu (Huawei)" > > uffd_move_pmd_test()/uffd_move_test_common() splits the test area into > chunks of chunk_size and moves them one by one. On arm64 with 64K base > pages the chunk_size (read_pmd_pagesize()) is 512MB, which is larger than > the whole 32MB (UFFD_TEST_MEM_SIZE) test area: > > step_count = nr_pages / (chunk_size / page_size) == 0 > > Because chunk_size > page_size, the test then aligns both areas up to > 512MB, which points far outside of the 32MB mappings, and decrements > step_count, which underflows to ULONG_MAX. The verification loop then > runs away and the first dereference of area_src faults with a SIGSEGV. > > Skip the test when a single chunk cannot fit into the test area. That leaves 64k untested, though? Why not adjust the chunk size accordingly? -- Cheers, David