From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 9EBDF1C0DF8 for ; Tue, 6 Aug 2024 11:02:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722942159; cv=none; b=DJw7oMMn1za3BtPqggwgvSF4w1HMPKEy8hf1fX+EaAfFXJiPjKbmuOnvkZonJ0wPwkHWWb5dLby7S4kgRD9Azqxg4c8JVRxCPSUt+98b6DT2AYVM37g36765ye5ZQ7d8VxpBQKhaiiqZm53XZL/wBZsqS2uzWODIjc4yR1wmgT4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722942159; c=relaxed/simple; bh=WPIwI17hwcZxWai6yGSu9rydstpOwlzbWRHp6gl8JV8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G2NrcfN/M0ofv8l0knSDBeJq3C6F2MLW7hdPAMb2uwba0AvDKaTRVzBM/allphXE5HbJaE8cP1VrYQ8/HyllgnYwVD6eGaOwD823pQxQcCVncblIpOeuk2xYbWl1tX4cyyO2xCsipv985Is4x/Mvu8YpvGMaTgn2UoHFbyTfDMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=YEW1ZGvx; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YEW1ZGvx" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722942156; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dG/wdq4KNgGfbSlTIoCrxrVcBX6174acHdMyq7P0THM=; b=YEW1ZGvxGEz+uefnqhgmYapIzPpTv68plgqESObYixGo+ipXFN6RloLOiqmnPfofVzGeaP 6FNkhqVhKSa2qj9kcsKwaYe0w1NNzv/TMVu47tIVESThLcNI6bsCk73VBOOHU3YNxrIwZR sYfhoMzrkuts/DdowezD7/9a56X0J9Y= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-396-jCS_w4KXPe60S2XtvRMnDA-1; Tue, 06 Aug 2024 07:02:33 -0400 X-MC-Unique: jCS_w4KXPe60S2XtvRMnDA-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CCB6B1955D44; Tue, 6 Aug 2024 11:02:31 +0000 (UTC) Received: from localhost (unknown [10.72.112.21]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8128319560AE; Tue, 6 Aug 2024 11:02:29 +0000 (UTC) Date: Tue, 6 Aug 2024 19:02:20 +0800 From: Baoquan He To: "Russell King (Oracle)" Cc: Jinjie Ruan , akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] ARM: Support allocating crashkernel above 4G for LPAE Message-ID: References: <20240802092510.3915986-1-ruanjinjie@huawei.com> <6c0a45c3-08a2-f889-9e66-ab8aff66ae8c@huawei.com> <8f051483-46be-87b6-03bb-5e0d145a2ac3@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 08/06/24 at 09:34am, Russell King (Oracle) wrote: > On Tue, Aug 06, 2024 at 04:11:30PM +0800, Baoquan He wrote: > > I am fine with it. BUT have you addressed Russell's concern, e.g how to > > test it actually? > > Thanks for bringing that up. > > Let me reinforce my position on this. I will _not_ be accepting a patch > that allows the crash kernel to be placed into high memory on 32-bit > ARM unless it has been thoroughly tested to prove that it can actually > work. > > Right now, I don't believe it can work as placing the kernel in highmem > likely means it will be located *outside* of the lower 4GiB of physical > memory which is all that will be accessible when the MMU is turned off. > This is a pre-condition to boot a kernel - the kernel image _must_ be > located within a region of memory which is exposed to the CPU when the > MMU is turned off. > > Unless it can be proven that placing the kernel in highmem means that > the kernel will be located in the lower 4GiB of physical memory space > with the MMU off, then further work on this patch is a waste of time. Yeah, totally agree.