From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 22D54155730 for ; Mon, 5 Aug 2024 13:18:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722863884; cv=none; b=sCQrMkIpKP6Zf/R5V52s+KQgxmqAFrDiKCS8ScEQb97rLd6DcH2ZrxkVBH8Iv+eYnlYKpcQtFCHixEUxD7deDrXt0fvCNPOqj8aZH/MGi5/x8xqysJa6CHHAzm2Wq3uQCw4VFUSH9jbjYo8kgARSSrgjb0KgEsvs0yjNVHIjb2s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722863884; c=relaxed/simple; bh=SvevPXi9fnjccO/eYyIhE7f24dWlC/0t/3PFVnasmbw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=H2F8CEUcIyB5cPMiYEE4IOSleFXvHLGRzXTYgoYGtm7aF+gsx2N3W55At1jR0OvsxQlrTbAJnl816HcQrbk0268f8PLFBl9J5VgDJxxue0Vg22ooJ891BfFa8090jkkt2tiMVFaWBUWaaPX6vMQcoIAj/uFt/JjpbgVFz3cdMi4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7B640C32782; Mon, 5 Aug 2024 13:18:02 +0000 (UTC) Date: Mon, 5 Aug 2024 14:18:00 +0100 From: Catalin Marinas To: "Russell King (Oracle)" Cc: Jinjie Ruan , bhe@redhat.com, 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> 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: On Fri, Aug 02, 2024 at 12:01:43PM +0100, Russell King wrote: > On Fri, Aug 02, 2024 at 05:25:10PM +0800, Jinjie Ruan wrote: > > As ARM LPAE feature support accessing memory beyond the 4G limit, define > > HAVE_ARCH_CRASHKERNEL_RESERVATION_HIGH macro to support reserving crash At least in 6.11-rc1, there's no trace of such macro anywhere. So not sure this patch has any effect (I haven't checked linux-next though). > > memory above 4G for ARM32 LPAE. > > > > No test because there is no LPAE ARM32 hardware. > > Why are you submitting patches for features you can't test? > > I'm not going to apply this without it being properly tested, because I > don't believe that this will work in the generic case. > > If the crash kernel is located in memory outside of the lower 4GiB of > address space, and there is no alias within physical address space > for that memory, then there is *no* *way* for such a kernel to boot. > > So, right now I believe this patch to be *fundamentally* wrong. Indeed. Even on arm64, we keep some crashkernel reservations in the lower parts of the memory for ZONE_DMA allocations. On arch/arm with LPAE, we could do something similar like forcing some lowmem reservation and allowing explicit allocation in the higher ranges with crashkernel=,high. We should, of course, force the kdump image placement in the lower memory. The user kexec tools must be taught to interpret this information and provide a DT accordingly to the crash kernel. -- Catalin