From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1050.oracle.com (aserp1050.oracle.com [141.146.126.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xN4mn0m7pzDqnl for ; Thu, 3 Aug 2017 06:39:36 +1000 (AEST) Received: from aserp1040.oracle.com (aserp1040.oracle.com [141.146.126.69]) by aserp1050.oracle.com (Sentrion-MTA-4.3.2/Sentrion-MTA-4.3.2) with ESMTP id v72KdXPT003051 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 2 Aug 2017 20:39:33 GMT From: Pavel Tatashin To: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, kasan-dev@googlegroups.com, borntraeger@de.ibm.com, heiko.carstens@de.ibm.com, davem@davemloft.net, willy@infradead.org, mhocko@kernel.org Subject: [v4 01/15] x86/mm: reserve only exiting low pages Date: Wed, 2 Aug 2017 16:38:10 -0400 Message-Id: <1501706304-869240-2-git-send-email-pasha.tatashin@oracle.com> In-Reply-To: <1501706304-869240-1-git-send-email-pasha.tatashin@oracle.com> References: <1501706304-869240-1-git-send-email-pasha.tatashin@oracle.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Struct pages are initialized by going through __init_single_page(). Since the existing physical memory in memblock is represented in memblock.memory list, struct page for every page from this list goes through __init_single_page(). The second memblock list: memblock.reserved, manages the allocated memory. The memory that won't be available to kernel allocator. So, every page from this list goes through reserve_bootmem_region(), where certain struct page fields are set, the assumption being that the struct pages have been initialized beforehand. In trim_low_memory_range() we unconditionally reserve memoryfrom PFN 0, but memblock.memory might start at a later PFN. For example, in QEMU, e820__memblock_setup() can use PFN 1 as the first PFN in memblock.memory, so PFN 0 is not on memblock.memory (and hence isn't initialized via __init_single_page) but is on memblock.reserved (and hence we set fields in the uninitialized struct page). Currently, the struct page memory is always zeroed during allocation, which prevents this problem from being detected. But, if some asserts provided by CONFIG_DEBUG_VM_PGFLAGS are tighten, this problem may become visible in existing kernels. In this patchset we will stop zeroing struct page memory during allocation. Therefore, this bug must be fixed in order to avoid random assert failures caused by CONFIG_DEBUG_VM_PGFLAGS triggers. The fix is to reserve memory from the first existing PFN. Signed-off-by: Pavel Tatashin Reviewed-by: Steven Sistare Reviewed-by: Daniel Jordan Reviewed-by: Bob Picco --- arch/x86/kernel/setup.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c index 3486d0498800..489cdc141bcb 100644 --- a/arch/x86/kernel/setup.c +++ b/arch/x86/kernel/setup.c @@ -790,7 +790,10 @@ early_param("reservelow", parse_reservelow); static void __init trim_low_memory_range(void) { - memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE)); + unsigned long min_pfn = find_min_pfn_with_active_regions(); + phys_addr_t base = min_pfn << PAGE_SHIFT; + + memblock_reserve(base, ALIGN(reserve_low, PAGE_SIZE)); } /* -- 2.13.3