From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:49922 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727426AbhAVJTy (ORCPT ); Fri, 22 Jan 2021 04:19:54 -0500 Subject: Re: [PATCH V3 1/3] mm/memory_hotplug: Prevalidate the address range being added with platform References: <1610975582-12646-1-git-send-email-anshuman.khandual@arm.com> <1610975582-12646-2-git-send-email-anshuman.khandual@arm.com> From: David Hildenbrand Message-ID: <9916f217-ec29-33ff-a260-7a26792d23a1@redhat.com> Date: Fri, 22 Jan 2021 10:18:21 +0100 MIME-Version: 1.0 In-Reply-To: <1610975582-12646-2-git-send-email-anshuman.khandual@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit List-ID: To: Anshuman Khandual , linux-mm@kvack.org, akpm@linux-foundation.org, hca@linux.ibm.com, catalin.marinas@arm.com Cc: Oscar Salvador , Vasily Gorbik , Will Deacon , Ard Biesheuvel , Mark Rutland , linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org > +/* > + * Platforms should define arch_get_mappable_range() that provides > + * maximum possible addressable physical memory range for which the > + * linear mapping could be created. The platform returned address > + * range must adhere to these following semantics. > + * > + * - range.start <= range.end > + * - Range includes both end points [range.start..range.end] > + * > + * There is also a fallback definition provided here, allowing the > + * entire possible physical address range in case any platform does > + * not define arch_get_mappable_range(). > + */ > +struct range __weak arch_get_mappable_range(void) > +{ > + struct range memhp_range = { > + .start = 0UL, > + .end = -1ULL, > + }; > + return memhp_range; > +} > + > +struct range memhp_get_pluggable_range(bool need_mapping) > +{ > + const u64 max_phys = (1ULL << (MAX_PHYSMEM_BITS + 1)) - 1; Sorry, thought about that line a bit more, and I think this is just wrong (took me longer to realize as it should). The old code used this calculation to print the limit only (in a wrong way), let's recap: Assume MAX_PHYSMEM_BITS=32 max_phys = (1ULL << (32 + 1)) - 1 = 0x1ffffffffull; Ehm, these are 33 bit. OTOH, old code checked for if (max_addr >> MAX_PHYSMEM_BITS) { Which makes sense, because 0x1ffffffffull >> 32 = 1 results in "true", meaning it's to big, while 0xffffffffull >> 32 = 0 correctly results in "false", meaning the address is fine. So, this should just be const u64 max_phys = 1ULL << MAX_PHYSMEM_BITS; (similarly as calculated in virito-mem code, or in kernel/resource.c) > + struct range memhp_range; > + > + if (need_mapping) { > + memhp_range = arch_get_mappable_range(); > + if (memhp_range.start > max_phys) { > + memhp_range.start = 0; > + memhp_range.end = 0; > + } > + memhp_range.end = min_t(u64, memhp_range.end, max_phys); > + } else { > + memhp_range.start = 0; > + memhp_range.end = max_phys; > + } > + return memhp_range; > +} > +EXPORT_SYMBOL_GPL(memhp_get_pluggable_range); -- Thanks, David / dhildenb