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 4DBE235E1A9 for ; Mon, 31 Aug 2026 06:16:18 +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=1788156979; cv=none; b=MVlqPZ9KenkYWVfUxs6JwGTLxAdriaA8CpWxnYYNXviJJvtbshQbxjnqChmY3OFbRdn5FujjouZL0xUebTUmWbl7Ba9CQy6qDbvxfGoTKo2CBc2n2jHhMzhc26ZdLXlCTH1NeNRMihmzQlV1CRHNcS68MNEIxLafH++pOSXFECs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788156979; c=relaxed/simple; bh=s9OINHCECiugw6Bxleag8Ex/yIbXRXGyauw5I/9QSdc=; h=MIME-Version:Date:From:To:Cc:Message-Id:In-Reply-To:References: Subject:Content-Type; b=l4kLo3aI2++8oozGSqq18t8pIrX/it163HHfkYoARGe3MmgWALsbFiFZM+UGxzK+x1WSqka2/C0Ja7SoginDJzd9WZRHA/M72cd6Sz18RKHIOi6ARLAiVJ+nG3eiodlEZhKzxE8mu66cs52XYTG42BYjTqmyUVfxU+3Fvgd3NY8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mknXiB5W; 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="mknXiB5W" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 631651F000E9; Mon, 31 Aug 2026 06:16:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788156978; bh=nQ1mOUazk5upCwE99RY/bxkx1ogD35Z5ZprZqBWTmPY=; h=Date:From:To:Cc:In-Reply-To:References:Subject; b=mknXiB5Wx4PX614tqvlG5yEzEYhGj7zNdApSg1s/xb7+xe1cqik9uWHFoRUttQTN8 GLbG4REFR4A6flpaaTQXrjNUZevMoY6CBXixEt5LvXCIRxJrQfYrcjAlVpjZAWaH0I DOCSmM/BGDIdrIlnVhwX5xef51ABfjYrQFODHTckOvzxD7JwPV7kIb8pdQhuww32o4 RDwm6xhsn21sGYPg0qO5bEJxfCfpOkpwZKQuq0sf/zSAS/VBd9oT27QLqnkrSlo8pS O3s9R2/qj4UzfBRiK2EvfDhxWm5nUqEOiDh0fmAIxR5cLV7JkPbUBvR6F+wVEEzGFM BXkPNPpKyyYVQ== Received: from ams-compute-02.internal (ams-compute-02.internal [10.64.2.62]) by mailfauth.ams.internal (Postfix) with ESMTP id B8903198006B; Mon, 31 Aug 2026 02:16:15 -0400 (EDT) Received: from ams-imap-11 ([10.64.2.31]) by ams-compute-02.internal (MEProxy); Mon, 31 Aug 2026 02:16:15 -0400 X-ME-Sender: X-ME-Proxy-Cause: dmFkZTGRWh3uAKJSJ4fzX7rQUTkRM0ok+x/9RVY95O3Kt4edIQPIo1yJqgLo4+wl9GIaUM Wf8bZrzB15C1S53cXh2wjZRLf2q/UgVT1n5TsW7zTfa3WG65q87zeGcgvWR0AgpkKuJ4LY sJ2CIIYGo/xMIC692J/5sSbaE6Zuwi2J0VQpbRvGreXOZ3QyH3CY2i1gFm6e7QbyDW4bdv XpRpoi+TP0awhJOXN0sIHbiLb+aJCUr2C1r9+Awi9h0sSAUAlYyp8zsbKIGINIqe4Cnk8c tsshHKB+sXTCCUw9lgMoozWSOKPArHEJ4wbyK7YGlnZlUf9j/531J8moto0g/EMln/JMQE S7gQiRYEpv5NiofMsAEWSr9F1A3Xaud8jtXNZUlNPNO58ewVHnaXAQkp2enfpiF6zSJ/sp UX/JyD2c6L/lPsj0KTaJvnLbZN3GpZKQYaipS3QwUdez3c3vi44ypBHxlCyy79NwUuDSFF td9jmitMJCFRHcrJQ+0GZH/zSMzj+TuMC6cDUNfaewl1USOVroOxyZB2ESZ1aGvoBXHJd9 0sdZmP7D1JxqyNm2WgNcSs4wQF/NFl7NYTKUQjYaWbzGjkKVmJQ1dxKuH4ogl7jmCUVUz0 w0FyFcBFGqdfzn6/o4+rB9QoR+z1Dp7h8IS6TjRMgp4kAMWisJx3rZC3suYg X-ME-Proxy: Feedback-ID: ice86485a:Fastmail Received: by mailuser.ams.internal (Postfix, from userid 501) id A90ACF8007B; Mon, 31 Aug 2026 02:16:12 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Mon, 31 Aug 2026 08:15:52 +0200 From: "Ard Biesheuvel" To: "Greg Kroah-Hartman" , "Karl Mehltretter" Cc: stable@vger.kernel.org, "Catalin Marinas" , "Will Deacon" , "Ryan Roberts" , "Mark Rutland" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Message-Id: <7f744f2a-409b-454f-bdb9-fccb5031640d@app.fastmail.com> In-Reply-To: <2026083125-upbeat-series-9565@gregkh> References: <20260831054247.33352-1-kmehltretter@gmail.com> <2026083125-upbeat-series-9565@gregkh> Subject: Re: [PATCH 6.6.y] arm64: mm: clear extra idmap level before use Content-Type: text/plain Content-Transfer-Encoding: 7bit On Mon, 31 Aug 2026, at 07:54, Greg Kroah-Hartman wrote: > On Mon, Aug 31, 2026 at 07:42:47AM +0200, Karl Mehltretter wrote: >> The 6.6.y adaptation of commit 0e9df1c905d8 ("arm64: mm: Don't remap >> pgtables for allocate vs populate") removes the clearing performed by >> early_pgtable_alloc(). Its replacement clears allocations made by the >> generic page-table walkers, but 6.6's create_idmap() still allocates an >> extra root level directly when a sub-48-bit VA kernel is loaded >> sufficiently high in physical memory. >> >> memblock_phys_alloc_range() does not zero the returned memory. The direct >> caller therefore publishes an uncleared root page and passes it to >> __create_pgd_mapping(). A stale nonzero entry can trip the bad-descriptor >> BUG_ON or be followed as a page-table descriptor, preventing the kernel >> from booting. >> >> Clear the direct allocation through its linear alias before publishing it. >> init_clear_pgtable() also supplies the barrier required before the table >> descriptor becomes visible. >> >> Mainline is not affected because commit e6128a8e523c ("arm64: mm: Use >> 48-bit virtual addressing for the permanent ID map") removed the dynamic >> extra level before page-table initialization moved out of the allocator. > > Why can't we take that change instead? > Nope. That relies on a massive refactoring of the arm64 startup code. Can we just revert 0e9df1c905d8 (aka 54322d95309d) instead?