From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04E48C28CC5 for ; Wed, 5 Jun 2019 16:30:07 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C718B206C3 for ; Wed, 5 Jun 2019 16:30:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="nfILlyOd" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C718B206C3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Snib70lejWUBunsVzD7vt/X98tgYnIHy5q/e6glnr08=; b=nfILlyOdjbcfjI vVHDLRjKMQRL2kxjc0910RZ165lm+xB+0vRVdFfVzKeRXzqz0xD12ajFGd5ATvYAx8ngNeRBdewyC XkXy4RljWS9YLFutlhIrPJHNn6j2/XkDSHOQa4uNx4Mp40/J9nsFHpRa1IiwqxoSWai9IosuAWtXL W/hX1C45YuYo46GP9d1XIEEnIzVFYt/nylKsD0qhQK4XrBd3GjQ7iT5VcoXCvI5MUmSRjlYzYQgwj Gql9L3zN263ju5D2PIOu/D+cZj1Q+nwPsx9TyH6qPtWhExSIKkeJYUoADjv1/WCd5tVQjg7JNXhNn bgK3dD4B+DpIvat/QyWg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hYYnc-0002Fr-Op; Wed, 05 Jun 2019 16:30:04 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hYYnY-00021N-0B; Wed, 05 Jun 2019 16:30:01 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 90C74374; Wed, 5 Jun 2019 09:29:59 -0700 (PDT) Received: from [10.1.196.105] (eglon.cambridge.arm.com [10.1.196.105]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A90FC3F5AF; Wed, 5 Jun 2019 09:29:56 -0700 (PDT) Subject: Re: [PATCH 2/4] arm64: kdump: support reserving crashkernel above 4G To: Chen Zhou References: <20190507035058.63992-1-chenzhou10@huawei.com> <20190507035058.63992-3-chenzhou10@huawei.com> From: James Morse Message-ID: Date: Wed, 5 Jun 2019 17:29:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190507035058.63992-3-chenzhou10@huawei.com> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190605_093000_241230_E1F80EDF X-CRM114-Status: GOOD ( 25.65 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: wangkefeng.wang@huawei.com, horms@verge.net.au, ard.biesheuvel@linaro.org, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, rppt@linux.ibm.com, linux-mm@kvack.org, takahiro.akashi@linaro.org, mingo@redhat.com, bp@alien8.de, ebiederm@xmission.com, kexec@lists.infradead.org, akpm@linux-foundation.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hello, On 07/05/2019 04:50, Chen Zhou wrote: > When crashkernel is reserved above 4G in memory, kernel should > reserve some amount of low memory for swiotlb and some DMA buffers. > Meanwhile, support crashkernel=X,[high,low] in arm64. When use > crashkernel=X parameter, try low memory first and fall back to high > memory unless "crashkernel=X,high" is specified. What is the 'unless crashkernel=...,high' for? I think it would be simpler to relax the ARCH_LOW_ADDRESS_LIMIT if reserve_crashkernel_low() allocated something. This way "crashkernel=1G" tries to allocate 1G below 4G, but fails if there isn't enough memory. "crashkernel=1G crashkernel=16M,low" allocates 16M below 4G, which is more likely to succeed, if it does it can then place the 1G block anywhere. > diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c > index 413d566..82cd9a0 100644 > --- a/arch/arm64/kernel/setup.c > +++ b/arch/arm64/kernel/setup.c > @@ -243,6 +243,9 @@ static void __init request_standard_resources(void) > request_resource(res, &kernel_data); > #ifdef CONFIG_KEXEC_CORE > /* Userspace will find "Crash kernel" region in /proc/iomem. */ > + if (crashk_low_res.end && crashk_low_res.start >= res->start && > + crashk_low_res.end <= res->end) > + request_resource(res, &crashk_low_res); > if (crashk_res.end && crashk_res.start >= res->start && > crashk_res.end <= res->end) > request_resource(res, &crashk_res); With both crashk_low_res and crashk_res, we end up with two entries in /proc/iomem called "Crash kernel". Because its sorted by address, and kexec-tools stops searching when it find "Crash kernel", you are always going to get the kernel placed in the lower portion. I suspect this isn't what you want, can we rename crashk_low_res for arm64 so that existing kexec-tools doesn't use it? > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > index d2adffb..3fcd739 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -74,20 +74,37 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init; > static void __init reserve_crashkernel(void) > { > unsigned long long crash_base, crash_size; > + bool high = false; > int ret; > > ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(), > &crash_size, &crash_base); > /* no crashkernel= or invalid value specified */ > - if (ret || !crash_size) > - return; > + if (ret || !crash_size) { > + /* crashkernel=X,high */ > + ret = parse_crashkernel_high(boot_command_line, > + memblock_phys_mem_size(), > + &crash_size, &crash_base); > + if (ret || !crash_size) > + return; > + high = true; > + } > > crash_size = PAGE_ALIGN(crash_size); > > if (crash_base == 0) { > - /* Current arm64 boot protocol requires 2MB alignment */ > - crash_base = memblock_find_in_range(0, ARCH_LOW_ADDRESS_LIMIT, > - crash_size, SZ_2M); > + /* > + * Try low memory first and fall back to high memory > + * unless "crashkernel=size[KMG],high" is specified. > + */ > + if (!high) > + crash_base = memblock_find_in_range(0, > + ARCH_LOW_ADDRESS_LIMIT, > + crash_size, CRASH_ALIGN); > + if (!crash_base) > + crash_base = memblock_find_in_range(0, > + memblock_end_of_DRAM(), > + crash_size, CRASH_ALIGN); > if (crash_base == 0) { > pr_warn("cannot allocate crashkernel (size:0x%llx)\n", > crash_size); > @@ -105,13 +122,18 @@ static void __init reserve_crashkernel(void) > return; > } > > - if (!IS_ALIGNED(crash_base, SZ_2M)) { > + if (!IS_ALIGNED(crash_base, CRASH_ALIGN)) { > pr_warn("cannot reserve crashkernel: base address is not 2MB aligned\n"); > return; > } > } > memblock_reserve(crash_base, crash_size); > > + if (crash_base >= SZ_4G && reserve_crashkernel_low()) { > + memblock_free(crash_base, crash_size); > + return; This is going to be annoying on platforms that don't have, and don't need memory below 4G. A "crashkernel=...,low" on these system will break crashdump. I don't think we should expect users to know the memory layout. (I'm assuming distro's are going to add a low reservation everywhere, just in case) I think the 'low' region should be a small optional/best-effort extra, that kexec-tools can't touch. I'm afraid you've missed the ugly bit of the crashkernel reservation... arch/arm64/mm/mmu.c::map_mem() marks the crashkernel as 'nomap' during the first pass of page-table generation. This means it isn't mapped in the linear map. It then maps it with page-size mappings, and removes the nomap flag. This is done so that arch_kexec_protect_crashkres() and arch_kexec_unprotect_crashkres() can remove the valid bits of the crashkernel mapping. This way the old-kernel can't accidentally overwrite the crashkernel. It also saves us if the old-kernel and the crashkernel use different memory attributes for the mapping. As your low-memory reservation is intended to be used for devices, having it mapped by the old-kernel as cacheable memory is going to cause problems if those CPUs aren't taken offline and go corrupting this memory. (we did crash for a reason after all) I think the simplest thing to do is mark the low region as 'nomap' in reserve_crashkernel() and always leave it unmapped. We can then describe it via a different string in /proc/iomem, something like "Crash kernel (low)". Older kexec-tools shouldn't use it, (I assume its not using strncmp() in a way that would do this by accident), and newer kexec-tools can know to describe it in the DT, but it can't write to it. Thanks, James _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel