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Thu, 28 May 2020 05:08:42 -0400 X-MC-Unique: DWq_gMhDOqG10yTCeTMvIQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2ECBA460; Thu, 28 May 2020 09:08:41 +0000 (UTC) Received: from [10.36.114.114] (ovpn-114-114.ams2.redhat.com [10.36.114.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2100E5D9EF; Thu, 28 May 2020 09:08:38 +0000 (UTC) Subject: Re: [PATCH] mm/compaction: Fix the incorrect hole in fast_isolate_freepages() To: Baoquan He Cc: Mike Rapoport , mgorman@suse.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, cai@lca.pw, mhocko@kernel.org, steve.wahl@hpe.com References: <20200521014407.29690-1-bhe@redhat.com> <20200521092612.GP1059226@linux.ibm.com> <20200521155225.GA20045@MiWiFi-R3L-srv> <20200521171836.GU1059226@linux.ibm.com> <20200522070114.GE26955@MiWiFi-R3L-srv> <20200522072524.GF26955@MiWiFi-R3L-srv> <20200522142053.GW1059226@linux.ibm.com> <20200526084543.GG26955@MiWiFi-R3L-srv> <20200526113244.GH13212@linux.ibm.com> <01beec81-565f-d335-5eff-22693fc09c0e@redhat.com> <20200528090731.GI20045@MiWiFi-R3L-srv> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200528090731.GI20045@MiWiFi-R3L-srv> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Rspamd-Queue-Id: E34E41803A188 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 28.05.20 11:07, Baoquan He wrote: > On 05/26/20 at 01:49pm, David Hildenbrand wrote: >> On 26.05.20 13:32, Mike Rapoport wrote: >>> Hello Baoquan, >>> >>> On Tue, May 26, 2020 at 04:45:43PM +0800, Baoquan He wrote: >>>> On 05/22/20 at 05:20pm, Mike Rapoport wrote: >>>>> Hello Baoquan, >>>>> >>>>> On Fri, May 22, 2020 at 03:25:24PM +0800, Baoquan He wrote: >>>>>> On 05/22/20 at 03:01pm, Baoquan He wrote: >>>>>>> >>>>>>> So let's add these unavailable ranges into memblock and reserve them >>>>>>> in init_unavailable_range() instead. With this change, they will be added >>>>>>> into appropriate node and zone in memmap_init(), and initialized in >>>>>>> reserve_bootmem_region() just like any other memblock reserved regions. >>>>>> >>>>>> Seems this is not right. They can't get nid in init_unavailable_range(). >>>>>> Adding e820 ranges may let them get nid. But the hole range won't be >>>>>> added to memblock, and still has the issue. >>>>>> >>>>>> Nack this one for now, still considering. >>>>> >>>>> Why won't we add the e820 reserved ranges to memblock.memory during >>>>> early boot as I suggested? >>>>> >>>>> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c >>>>> index c5399e80c59c..b0940c618ed9 100644 >>>>> --- a/arch/x86/kernel/e820.c >>>>> +++ b/arch/x86/kernel/e820.c >>>>> @@ -1301,8 +1301,11 @@ void __init e820__memblock_setup(void) >>>>> if (end != (resource_size_t)end) >>>>> continue; >>>>> >>>>> - if (entry->type == E820_TYPE_SOFT_RESERVED) >>>>> + if (entry->type == E820_TYPE_SOFT_RESERVED || >>>>> + entry->type == E820_TYPE_RESERVED) { >>>>> + memblock_add(entry->addr, entry->size); >>>>> memblock_reserve(entry->addr, entry->size); >>>>> + } >>>>> >>>>> if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN) >>>>> continue; >>>>> >>>>> The setting of node later in numa_init() will assign the proper node >>>>> for these regions as it does for the usable memory. >>>> >>>> Yes, if it's only related to e820 reserved region, this truly works. >>>> >>>> However, it also has ACPI table regions. That's why I changed to call >>>> the problematic area as firmware reserved ranges later. >>>> >>>> Bisides, you can see below line, there's another reserved region which only >>>> occupies one page in one memory seciton. If adding to memblock.memory, we also >>>> will build struct mem_section and the relevant struct pages for the whole >>>> section. And then the holes around that page will be added and initialized in >>>> init_unavailable_mem(). numa_init() will assign proper node for memblock.memory >>>> and memblock.reserved, but won't assign proper node for the holes. >>>> >>>> ~~~ >>>> [ 0.000000] BIOS-e820: [mem 0x00000000fed80000-0x00000000fed80fff] reserved >>>> ~~~ >>>> >>>> So I still think we should not add firmware reserved range into >>>> memblock for fixing this issue. >>>> >>>> And, the fix in the original patch seems necessary. You can see in >>>> compaction code, the migration source is chosen from LRU pages or >>>> movable pages, the migration target has to be got from Buddy. However, >>>> only the min_pfn in fast_isolate_freepages(), it's calculated by >>>> distance between cc->free_pfn - cc->migrate_pfn, we can't guarantee it's >>>> safe, then use it as the target to handle. >>> >>> I do not object to your original fix with careful check for pfn validity. >>> >>> But I still think that the memory reserved by the firmware is still >>> memory and it should be added to memblock.memory. This way the memory >> >> If it's really memory that could be read/written, I think I agree. > > I would say some of them may not be allowed to be read/written, if I > understand it correctly. I roughly went through the x86 init code, there > are some places where mem region is marked as E820_TYPE_RESERVED so that > they are not touched after initialization. E.g: > > 1) pfn 0 > In trim_bios_range(), we set the pfn 0 as E820_TYPE_RESERVED. You can > see the code comment, this is a BIOS owned area, but not kernel RAM. > > 2)GART reserved region > In early_gart_iommu_check(), GART IOMMU firmware will reserve a region > in an area, firmware designer won't map system RAM into that area. > > And also intel_graphics_stolen(), arch_rmrr_sanity_check(), these > regions are not system RAM backed area, reading from or writting into > these area may cause error. > > Futhermore, there's a KASLR bug found by HPE, its triggering and root > cause are written into below commit log. You can see that accessing to > firmware reserved region caused BIOS to halt system when cpu doing > speculative. > > commit 2aa85f246c181b1fa89f27e8e20c5636426be624 > Author: Steve Wahl > Date: Tue Sep 24 16:03:55 2019 -0500 > > x86/boot/64: Make level2_kernel_pgt pages invalid outside kernel area > > Our hardware (UV aka Superdome Flex) has address ranges marked > reserved by the BIOS. Access to these ranges is caught as an error, > causing the BIOS to halt the system. > >> >>> map will be properly initialized from the very beginning and we won't >>> need init_unavailable_mem() and alike workarounds and. Obviously, the patch >> >> I remember init_unavailable_mem() is necessary for holes within >> sections, where we actually *don't* have memory, but we still have have >> a valid memmap (full section) that we have to initialize. >> >> See the example from 4b094b7851bf ("mm/page_alloc.c: initialize memmap >> of unavailable memory directly"). Our main memory ends within a section, >> so we have to initialize the remaining parts because the whole section >> will be marked valid/online. > > Yes, memory hole need be handled in init_unavailable_mem(). Since we > have created struct page for them, need initialize them. We can't > discard init_unavailable_mem() for now. > >> >> Any way to improve this handling is appreciated. In that patch I also >> spelled out that we might want to mark such holes via a new page type, >> e.g., PageHole(). Such a page is a memory hole, but has a valid memmap. >> Any content in the memmap (zone/node) should be ignored. > > As I said at above, I am a little conservative to add all those regions of > E820_TYPE_RESERVED into memblock.memory and memblock.reserved, because > most of them are firmware reserved region, they may be not backed by normal > RAM. > > I was thinking to step back to use mm_zero_struct_page() inside > init_unavailable_range() as below. But it doesn't differ much > from __init_single_page(), except of the _refcount and mapcount. > Zeroing struct page equals to putting them into node 0, zero 0. > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3973b5fdfe3f..4e4b72cf5283 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6901,7 +6901,7 @@ static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn) > * (in memblock.reserved but not in memblock.memory) will > * get re-initialized via reserve_bootmem_region() later. > */ > - __init_single_page(pfn_to_page(pfn), pfn, 0, 0); > + mm_zero_struct_page(pfn_to_page(pfn)); > __SetPageReserved(pfn_to_page(pfn)); > pgcnt++; > } > > About adding these unavailable ranges into node/zone, in the old code, > it just happened to add them into expected node/zone. You can see in > early_pfn_in_nid(), if no nid found from memblock, the returned '-1' > will make it true ironically. But that is not saying the bad thing > always got good result. If the last zone of node 0 is DMA32 zone, the > deferred init will skip the only chance to add some of unavailable > rnages into expected node/zone. Means they were not always added into > appropriate node/zone before, the change of iterating memblock.memory in > memmap_init() dones't introduce regression. > > static inline bool __meminit early_pfn_in_nid(unsigned long pfn, int node) > { > int nid; > > nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache); > if (nid >= 0 && nid != node) > return false; > return true; > } > > So if no anybody need access them after boot, not adding them into any > node/zone sounds better. Otherwise, better add them in the appropriate > node/zone. Yes, the node/zone is just completely irrelevant for these pages I'd say. As I said, maybe we can flag these memmaps somehow as "while this is an initialized memmap, the node/zone is garbage and this memmap should just be ignored completely in any kind of node/zone aware code". -- Thanks, David / dhildenb