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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 463BEC433F5 for ; Thu, 17 Feb 2022 10:50:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239330AbiBQKuU (ORCPT ); Thu, 17 Feb 2022 05:50:20 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:42746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234328AbiBQKuS (ORCPT ); Thu, 17 Feb 2022 05:50:18 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1470C1ED1E7 for ; Thu, 17 Feb 2022 02:50:04 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id B5E3DB82171 for ; Thu, 17 Feb 2022 10:50:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F75EC340E8; Thu, 17 Feb 2022 10:49:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1645095001; bh=V5/vdsYX/un8H0kUy8bihughcNy3eq6MQO+YbmfOOTs=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=JCv3V8gFFGQhVmq6dxfWkx+4qDh93wxw6pGplOggWfW2jWMKWc4SQ/WS4pczozvzg mSC/GrCzDyuq1Cbyl6LNwYwZzknV8jhSHtL6gLYHIh7jqpu85RdOZoewW06sOL01ZO Dtk3oD5XJfk0scuSuG4eyIXC9c92cMu5VJFWHx+HSrWcwJuXftQN3Ob4M0Y9pahF+w nCG0DFuPs/a/ADCoiPbK6ZQM4GLrpMHMQ0vz7ubXFuqsYDjoR0359u7P/lBFYbWNwA O97i4LqWkIP3yGpqLIbVWscVGR2epy9KM9OYXDo/9LreHSlE/eb4GKOeakUc67Rdb/ 3XtQXV7Fb070A== Message-ID: Subject: Re: [PATCH] arm64: Do not defer reserve_crashkernel() for platforms with no DMA memory zones From: nicolas saenz julienne To: Vijay Balakrishna , Catalin Marinas , Will Deacon Cc: Anshuman Khandual , Mike Rapoport , Ard Biesheuvel , Pavel Tatashin , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Date: Thu, 17 Feb 2022 11:49:56 +0100 In-Reply-To: <1645056294-6509-1-git-send-email-vijayb@linux.microsoft.com> References: <1645056294-6509-1-git-send-email-vijayb@linux.microsoft.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-1.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2022-02-16 at 16:04 -0800, Vijay Balakrishna wrote: > The following patches resulted in deferring crash kernel reservation to > mem_init(), mainly aimed at platforms with DMA memory zones (no IOMMU), > in particular Raspberry Pi 4. > > commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32") > commit 8424ecdde7df ("arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges") > commit 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into mem_init()") > commit 2687275a5843 ("arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required") > > Above changes introduced boot slowdown due to linear map creation for > all the memory banks with NO_BLOCK_MAPPINGS, see discussion[1]. The proposed > changes restore crash kernel reservation to earlier behavior thus avoids > slow boot, particularly for platforms with IOMMU (no DMA memory zones). > > [1] https://lore.kernel.org/all/9436d033-579b-55fa-9b00-6f4b661c2dd7@linux.microsoft.com/ > > Signed-off-by: Vijay Balakrishna > Cc: stable@vger.kernel.org > --- > Tested changes to confirm no ~150ms boot slowdown on our SoC with IOMMU > and 8GB memory. Also tested with ZONE_DMA and/or ZONE_DMA32 configs to confirm > no regression to deferring scheme of crash kernel memory reservation. > In both cases successfully collected kernel crash dump. > --- > arch/arm64/mm/init.c | 14 +++++++++++--- > arch/arm64/mm/mmu.c | 24 +++++++++++++++++++++++- > 2 files changed, 34 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > index db63cc885771..f2a982c19b75 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -62,7 +62,11 @@ EXPORT_SYMBOL(memstart_addr); > * In such case, ZONE_DMA32 covers the rest of the 32-bit addressable memory, > * otherwise it is empty. > */ > -phys_addr_t arm64_dma_phys_limit __ro_after_init; > +#if !defined(CONFIG_ZONE_DMA) && !defined(CONFIG_ZONE_DMA32) > +phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1; > +#else > +phys_addr_t __ro_after_init arm64_dma_phys_limit; > +#endif > > #ifdef CONFIG_KEXEC_CORE > /* > @@ -153,8 +157,6 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max) > if (!arm64_dma_phys_limit) > arm64_dma_phys_limit = dma32_phys_limit; > #endif > - if (!arm64_dma_phys_limit) > - arm64_dma_phys_limit = PHYS_MASK + 1; > max_zone_pfns[ZONE_NORMAL] = max; > > free_area_init(max_zone_pfns); > @@ -315,6 +317,10 @@ void __init arm64_memblock_init(void) > > early_init_fdt_scan_reserved_mem(); > > +#if !defined(CONFIG_ZONE_DMA) && !defined(CONFIG_ZONE_DMA32) > + reserve_crashkernel(); > +#endif > + > high_memory = __va(memblock_end_of_DRAM() - 1) + 1; > } > > @@ -357,11 +363,13 @@ void __init bootmem_init(void) > */ > dma_contiguous_reserve(arm64_dma_phys_limit); > > +#if defined(CONFIG_ZONE_DMA) || defined(CONFIG_ZONE_DMA32) > /* > * request_standard_resources() depends on crashkernel's memory being > * reserved, so do it here. > */ > reserve_crashkernel(); > +#endif > > memblock_dump_all(); > } > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index acfae9b41cc8..e7faf5edccfc 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -517,7 +517,7 @@ static void __init map_mem(pgd_t *pgdp) > */ > BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end)); > > - if (can_set_direct_map() || crash_mem_map || IS_ENABLED(CONFIG_KFENCE)) > + if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) > flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; > > /* > @@ -528,6 +528,14 @@ static void __init map_mem(pgd_t *pgdp) > */ > memblock_mark_nomap(kernel_start, kernel_end - kernel_start); > > +#ifdef CONFIG_KEXEC_CORE > + if (crash_mem_map && !crashk_res.end) > + flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; Using IS_ENABLED(ZONE_DMA/DMA32) instead of '!crashk_res.end' would be more efficient and a bit more explicit IMO. > /* map all the memory banks */ > for_each_mem_range(i, &start, &end) { > if (start >= end) > @@ -554,6 +562,20 @@ static void __init map_mem(pgd_t *pgdp) > __map_memblock(pgdp, kernel_start, kernel_end, > PAGE_KERNEL, NO_CONT_MAPPINGS); > memblock_clear_nomap(kernel_start, kernel_end - kernel_start); > +#ifdef CONFIG_KEXEC_CORE > + /* > + * Use page-level mappings here so that we can shrink the region > + * in page granularity and put back unused memory to buddy system > + * through /sys/kernel/kexec_crash_size interface. > + */ > + if (crashk_res.end) { Same here. > + __map_memblock(pgdp, crashk_res.start, crashk_res.end + 1, > + PAGE_KERNEL, > + NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS); > + memblock_clear_nomap(crashk_res.start, > + resource_size(&crashk_res)); > + } > +#endif Now, I carefully reviewed the patch and it seems to be doing the right thing. But even while knowlegable on the topic, it took a good amount of effort to untangle the possible code paths. I suspect it's going to be painful to maintain. I'd suggest at least introducing a comment explaining the situation. If there approach if deemed acceptable, I'll test is on the RPi4. Regards, Nicolas