From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D64F9606A8B3 for ; Thu, 12 Nov 2026 14:29:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=GElljJ/b; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=fby67aXm 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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=sRazLDIEc7CMUp/9vgq2YR+tcffN4fGN/wRdKhy4qfE=; b=GElljJ/bXF5ATr9Y/Ph58kjmAI V0K7JCZai6lQFueDsS7sbLJnBEqPKXJJ2wTw9FBwxuAKUeFWjbrNRiE6P3N3ZB9MXwpfrcCdWWUPU m4lUbl6gFYd1RdlyOVcij+KFiCJk6ougt5lEdNpxTGMKRRIB4Uyu9F/q/U4Mx/AX9k+jo3cMUQxNg CQvZKaeNvMTv6XZY6bXf4e+NKGy776TGTyC7OGsET+Mj42TtokT61lbRX8CEWxGtvIlmZmdbA9PSe kjjZ0zdqjPDqkAx9b9A+ytRh1pJIyy9fkDWoBs8/AWs4J5GLPvyhz/nsYSBxAV+GyqItbOrZVTY0s uVlczgkQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRVne-0000000AGSl-246K; Thu, 12 Nov 2026 14:29:14 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRVnb-0000000AGS3-3R6E for linux-arm-kernel@lists.infradead.org; Thu, 12 Nov 2026 14:29:13 +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 E07A61477; Thu, 12 Nov 2026 06:29:07 -0800 (PST) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D93B83F673; Thu, 12 Nov 2026 06:29:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1794493750; bh=XiaNpbbvxm6cKE/zgmNwmyN9+sHlHIuKTGnW432EXr4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fby67aXmxYqsYQ+cJC3GcBthEnnJJfdGSIYm40Lcu20zGsDk9qauSSN3TVDH36s+A aizxncjEclC0Gap/jNtf43T4IKOjBghSsjwIFWshSDsu1J7xkfVFbrN8L9ZwyHuEn+ GCODgR3flC+q2PeYAw8JU5AHNQWkEmCxf053CvKo= Date: Thu, 12 Nov 2026 14:29:06 +0000 From: Catalin Marinas To: "Oscar Salvador (SUSE)" Cc: Chris Down , Will Deacon , linux-kernel@vger.kernel.org, kernel-team@meta.com, Mark Rutland , Huang Ying , Andrew Morton , Muchun Song , Oscar Salvador , David Hildenbrand , Mike Kravetz , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH] arm64: hugetlb: Prevent write fault livelocks on stale TLB entries Message-ID: References: X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261112_062911_979300_1F821036 X-CRM114-Status: GOOD ( 26.29 ) X-Spam-Score: -4.4 (----) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-10.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Nov 11, 2026 at 10:04:19AM +0100, Oscar Salvador (SUSE) wrote: > On Tue, Nov 10, 2026 at 08:39:02PM -0800, Chris Down wrote: > > In Meta production, we have had tasks get stuck in a fault loop while > > using hugetlb on arm64. During my investigations I found that affected > > tasks share a private hugetlb page. > > > > Looking at the stuck task states, I found the following ordering: > > > > CPU0 CPU1 > > ---- ---- > > read page > > [read only entry cached in TLB] > > write page > > hugetlb_fault() > > hugetlb_wp() > > [reuse folio] > > set_huge_ptep_maybe_writable() > > set_huge_ptep_writable() > > [flush local TLB only] > > > > write page using stale entry > > hugetlb_fault() > > huge_ptep_set_access_flags() > > [entry already writable, no flush] > > retry write using stale entry > > [fault indefinitely. well, that's not ideal!] > > > > The reason is that when a write fault makes a non-contiguous hugetlb > > entry writable, it only invalidates the local TLB. However, another CPU > > can keep the old read-only entry, so its write will fault even though > > the page table already permits it. hugetlb_fault() then finds nothing to > > change and leaves the stale entry in place, so the same write keeps > > going round in circles. > > > > This is particularly bad because, if the kernel is copying to user > > memory, the retry stays inside the kernel and the task can't act on the > > pending signal. > > > > It can even remain unkillable while holding locks across the copy, > > resulting in further failures. For example, a read into a hugetlb > > buffer can hold the pipe mutex and block other users of the pipe until > > the loop ends, causing cascading lockups across the machine. > > > > To fix this, when a write fault finds nothing to change in a > > non-contiguous hugetlb entry, let's invalidate the local entry. > > > > Fixes: cb1fa2e99955 ("arm64, tlbflush: don't TLBI broadcast if page reused in write fault") > > Cc: > > Signed-off-by: Chris Down > > This makes sense to me, and I see that commit cb1fa2e99955 ("arm64, tlbflush: > don't TLBI broadcast if page reused in write fault") only invalidated local tlb > for cont-hugetlb. > Reading the changelog, I guess that was an oversight because I could not find > the reason behind. I think you mean non-contiguous hugetlb here? cb1fa2e99955 switched __ptep_set_access_flags() to local invalidation, used on the non-contiguous hugetlb path. Contiguous hugetlb updates still broadcast through get_clear_contig_flush(). Ordinary contpte mappings also switched to local invalidation but those go through the generic fault handler and its fix_spurious_fault() fallback. That fallback is what the hugetlb path was missing. -- Catalin