From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id 750B76B0003 for ; Fri, 16 Feb 2018 15:40:08 -0500 (EST) Received: by mail-wr0-f199.google.com with SMTP id n50so2234667wrn.20 for ; Fri, 16 Feb 2018 12:40:08 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id v17si3270135wmh.154.2018.02.16.12.40.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Feb 2018 12:40:07 -0800 (PST) Date: Fri, 16 Feb 2018 12:40:04 -0800 From: Andrew Morton Subject: Re: [RESEND v2] mm: don't defer struct page initialization for Xen pv guests Message-Id: <20180216124004.8465f643a5539125d77ba79f@linux-foundation.org> In-Reply-To: <20180216154101.22865-1-jgross@suse.com> References: <20180216154101.22865-1-jgross@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Juergen Gross Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, xen-devel@lists.xenproject.org, mhocko@suse.com, stable@vger.kernel.org, Pavel Tatashin On Fri, 16 Feb 2018 16:41:01 +0100 Juergen Gross wrote: > Commit f7f99100d8d95dbcf09e0216a143211e79418b9f ("mm: stop zeroing > memory during allocation in vmemmap") broke Xen pv domains in some > configurations, as the "Pinned" information in struct page of early > page tables could get lost. This will lead to the kernel trying to > write directly into the page tables instead of asking the hypervisor > to do so. The result is a crash like the following: Let's cc Pavel, who authored f7f99100d8d95d. > [ 0.004000] BUG: unable to handle kernel paging request at ffff8801ead19008 > [ 0.004000] IP: xen_set_pud+0x4e/0xd0 > [ 0.004000] PGD 1c0a067 P4D 1c0a067 PUD 23a0067 PMD 1e9de0067 PTE 80100001ead19065 > [ 0.004000] Oops: 0003 [#1] PREEMPT SMP > [ 0.004000] Modules linked in: > [ 0.004000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-default+ #271 > [ 0.004000] Hardware name: Dell Inc. Latitude E6440/0159N7, BIOS A07 06/26/2014 > [ 0.004000] task: ffffffff81c10480 task.stack: ffffffff81c00000 > [ 0.004000] RIP: e030:xen_set_pud+0x4e/0xd0 > [ 0.004000] RSP: e02b:ffffffff81c03cd8 EFLAGS: 00010246 > [ 0.004000] RAX: 002ffff800000800 RBX: ffff88020fd31000 RCX: 0000000000000000 > [ 0.004000] RDX: ffffea0000000000 RSI: 00000001b8308067 RDI: ffff8801ead19008 > [ 0.004000] RBP: ffff8801ead19008 R08: aaaaaaaaaaaaaaaa R09: 00000000063f4c80 > [ 0.004000] R10: aaaaaaaaaaaaaaaa R11: 0720072007200720 R12: 00000001b8308067 > [ 0.004000] R13: ffffffff81c8a9cc R14: ffff88018fd31000 R15: 000077ff80000000 > [ 0.004000] FS: 0000000000000000(0000) GS:ffff88020f600000(0000) knlGS:0000000000000000 > [ 0.004000] CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 0.004000] CR2: ffff8801ead19008 CR3: 0000000001c09000 CR4: 0000000000042660 > [ 0.004000] Call Trace: > [ 0.004000] __pmd_alloc+0x128/0x140 > [ 0.004000] ? acpi_os_map_iomem+0x175/0x1b0 > [ 0.004000] ioremap_page_range+0x3f4/0x410 > [ 0.004000] ? acpi_os_map_iomem+0x175/0x1b0 > [ 0.004000] __ioremap_caller+0x1c3/0x2e0 > [ 0.004000] acpi_os_map_iomem+0x175/0x1b0 > [ 0.004000] acpi_tb_acquire_table+0x39/0x66 > [ 0.004000] acpi_tb_validate_table+0x44/0x7c > [ 0.004000] acpi_tb_verify_temp_table+0x45/0x304 > [ 0.004000] ? acpi_ut_acquire_mutex+0x12a/0x1c2 > [ 0.004000] acpi_reallocate_root_table+0x12d/0x141 > [ 0.004000] acpi_early_init+0x4d/0x10a > [ 0.004000] start_kernel+0x3eb/0x4a1 > [ 0.004000] ? set_init_arg+0x55/0x55 > [ 0.004000] xen_start_kernel+0x528/0x532 > [ 0.004000] Code: 48 01 e8 48 0f 42 15 a2 fd be 00 48 01 d0 48 ba 00 00 00 00 00 ea ff ff 48 c1 e8 0c 48 c1 e0 06 48 01 d0 48 8b 00 f6 c4 02 75 5d <4c> 89 65 00 5b 5d 41 5c c3 65 8b 05 52 9f fe 7e 89 c0 48 0f a3 > [ 0.004000] RIP: xen_set_pud+0x4e/0xd0 RSP: ffffffff81c03cd8 > [ 0.004000] CR2: ffff8801ead19008 > [ 0.004000] ---[ end trace 38eca2e56f1b642e ]--- > > Avoid this problem by not deferring struct page initialization when > running as Xen pv guest. > > ... > > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -347,6 +347,9 @@ static inline bool update_defer_init(pg_data_t *pgdat, > /* Always populate low zones for address-constrained allocations */ > if (zone_end < pgdat_end_pfn(pgdat)) > return true; > + /* Xen PV domains need page structures early */ > + if (xen_pv_domain()) > + return true; > (*nr_initialised)++; > if ((*nr_initialised > pgdat->static_init_pgcnt) && > (pfn & (PAGES_PER_SECTION - 1)) == 0) { I'm OK with applying the patch as a short-term regression fix but I do wonder whether it's the correct fix. What is special about Xen (in some configurations!) that causes it to find a hole in deferred initialization? I'd like us to delve further please. Because if Xen found a hole in the implementation, others might do so. Or perhaps Xen is doing something naughty. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org