From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gbyI5-0007VO-QW for kexec@lists.infradead.org; Wed, 26 Dec 2018 01:47:26 +0000 Date: Wed, 26 Dec 2018 09:47:01 +0800 From: Dave Young Subject: Re: [PATCHv2] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr Message-ID: <20181226014701.GD11472@dhcp-128-65.nay.redhat.com> References: <1544760446-506-1-git-send-email-kernelfans@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1544760446-506-1-git-send-email-kernelfans@gmail.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Pingfan Liu Cc: Baoquan He , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Andrew Morton , yinghai@kernel.org, vgoyal@redhat.com On 12/14/18 at 12:07pm, Pingfan Liu wrote: > Customer reported a bug on a high end server with many pcie devices, where > kernel bootup with crashkernel=384M, and kaslr is enabled. Even > though we still see much memory under 896 MB, the finding still failed > intermittently. Because currently we can only find region under 896 MB, > if w/0 ',high' specified. Then KASLR breaks 896 MB into several parts > randomly, and crashkernel reservation need be aligned to 128 MB, that's > why failure is found. It raises confusion to the end user that sometimes > crashkernel=X works while sometimes fails. > If want to make it succeed, customer can change kernel option to > "crashkernel=384M, high". Just this give "crashkernel=xx@yy" a very > limited space to behave even though its grammer looks more generic. > And we can't answer questions raised from customer that confidently: > 1) why it doesn't succeed to reserve 896 MB; > 2) what's wrong with memory region under 4G; > 3) why I have to add ',high', I only require 384 MB, not 3840 MB. > > This patch simplifies the method suggested in the mail [1]. It just goes > bottom-up to find a candidate region for crashkernel. The bottom-up may be > better compatible with the old reservation style, i.e. still want to get > memory region from 896 MB firstly, then [896 MB, 4G], finally above 4G. > > There is one trivial thing about the compatibility with old kexec-tools: > if the reserved region is above 896M, then old tool will fail to load > bzImage. But without this patch, the old tool also fail since there is no > memory below 896M can be reserved for crashkernel. > > [1]: http://lists.infradead.org/pipermail/kexec/2017-October/019571.html > Signed-off-by: Pingfan Liu > Cc: Dave Young > Cc: Andrew Morton > Cc: Baoquan He > Cc: yinghai@kernel.org, > Cc: vgoyal@redhat.com > Cc: kexec@lists.infradead.org > > --- > v1->v2: > improve commit log > arch/x86/kernel/setup.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index d494b9b..60f12c4 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -541,15 +541,18 @@ static void __init reserve_crashkernel(void) > > /* 0 means: find the address automatically */ > if (crash_base <= 0) { > + if (!memblock_bottom_up()) > + memblock_set_bottom_up(true); > /* > * Set CRASH_ADDR_LOW_MAX upper bound for crash memory, > * as old kexec-tools loads bzImage below that, unless > * "crashkernel=size[KMG],high" is specified. > */ > crash_base = memblock_find_in_range(CRASH_ALIGN, > - high ? CRASH_ADDR_HIGH_MAX > - : CRASH_ADDR_LOW_MAX, > - crash_size, CRASH_ALIGN); > + (max_pfn * PAGE_SIZE), crash_size, CRASH_ALIGN); > + if (!memblock_bottom_up()) > + memblock_set_bottom_up(false); The previous memblock_set_bottom_up(true) set it as true, so "!memblock_bottom_up()" is impossible, not sure what is the point of this condition check. Do you want to restore the original memblock direction? If so a variable to save the old direction is needed. But is this really necessary? Do you know any side effects of setting the bottom up as true? > + > if (!crash_base) { > pr_info("crashkernel reservation failed - No suitable area found.\n"); > return; > -- > 2.7.4 > > > _______________________________________________ > kexec mailing list > kexec@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/kexec Thanks Dave _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec