From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Rapoport Subject: Re: [PATCHv3 2/2] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr Date: Mon, 31 Dec 2018 10:46:09 +0200 Message-ID: <20181231084608.GB28478@rapoport-lnx> References: <1545966002-3075-1-git-send-email-kernelfans@gmail.com> <1545966002-3075-3-git-send-email-kernelfans@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1545966002-3075-3-git-send-email-kernelfans-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+glkk-kexec=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Pingfan Liu Cc: Michal Hocko , "Rafael J. Wysocki" , Stefan Agner , Tang Chen , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Yaowei Bai , Baoquan He , Jonathan Corbet , Pavel Tatashin , linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Dave Young , Daniel Vacek , vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Len Brown , Nicholas Piggin , Mike Rapoport , yinghai-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, Naoya Horiguchi , Mathieu Malaterre , kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton List-Id: linux-acpi@vger.kernel.org On Fri, Dec 28, 2018 at 11:00:02AM +0800, 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: Tang Chen > Cc: "Rafael J. Wysocki" > Cc: Len Brown > Cc: Andrew Morton > Cc: Mike Rapoport > Cc: Michal Hocko > Cc: Jonathan Corbet > Cc: Yaowei Bai > Cc: Pavel Tatashin > Cc: Nicholas Piggin > Cc: Naoya Horiguchi > Cc: Daniel Vacek > Cc: Mathieu Malaterre > Cc: Stefan Agner > Cc: Dave Young > Cc: Baoquan He > Cc: yinghai-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, > Cc: vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org > Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > --- > 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..165f9c3 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) { > + bool bottom_up = 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); > + memblock_set_bottom_up(bottom_up); Using bottom-up does not guarantee that the allocation won't fall into a removable memory, it only makes it highly probable. I think that the 'max_pfn * PAGE_SIZE' limit should be replaced with the end of the non-removable memory node. > + > if (!crash_base) { > pr_info("crashkernel reservation failed - No suitable area found.\n"); > return; > -- > 2.7.4 > -- Sincerely yours, Mike.