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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH -next resend v3] mm: hwposion: support recovery from ksm_might_need_to_copy() Content-Language: en-US To: Miaohe Lin , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "tony.luck@intel.com" , "linux-kernel@vger.kernel.org" , David Hildenbrand References: <20221213030557.143432-1-wangkefeng.wang@huawei.com> <20221213120523.141588-1-wangkefeng.wang@huawei.com> <20221216014729.GA2116060@hori.linux.bs1.fc.nec.co.jp> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4980E1C000A X-Rspam-User: X-Stat-Signature: pt5yqnshri8hzfcararb4dzmrt1qzi6c X-HE-Tag: 1675214612-139048 X-HE-Meta: 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 BaKe7I7N qRFk3ClkxWUczUHeVLJZD3xrIaNKnjnEKttc3olVGLe2TCHyghBSqArd9tMl8atvYTtc0v5k3H/eQid6Xm4hAbw1t3X4Ep50Ra1NaA/6haX6qUQJP0IXbR0PViUWGS7aSBEgfJLUlqUxXGUUzRD9J0JcGY5Z/FonG91Q7PRNWNk5I/yOBNGXzBvDdncLRXxd7qkzfx71J8RjYzda6pD9qrVWAGSReD9trMIwAkrAWIYHGwK4= 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 2022/12/17 10:24, Miaohe Lin wrote: > On 2022/12/16 9:47, HORIGUCHI NAOYA(堀口 直也) wrote: >> On Tue, Dec 13, 2022 at 08:05:23PM +0800, Kefeng Wang wrote: >>> When the kernel copy a page from ksm_might_need_to_copy(), but runs >>> into an uncorrectable error, it will crash since poisoned page is >>> consumed by kernel, this is similar to Copy-on-write poison recovery, >> >> Maybe you mean "this is similar to the issue recently fixed by >> Copy-on-write poison recovery."? And if this sentence ends here, >> please put "." instead of ",". >> >>> When an error is detected during the page copy, return VM_FAULT_HWPOISON >>> in do_swap_page(), and install a hwpoison entry in unuse_pte() when >>> swapoff, which help us to avoid system crash. Note, memory failure on >>> a KSM page will be skipped, but still call memory_failure_queue() to >>> be consistent with general memory failure process. >> >> Thank you for the work. I have a few comment below ... > > Thanks both. > >>> - if (unlikely(!PageUptodate(page))) { >>> - pte_t pteval; >>> + if (hwposioned || !PageUptodate(page)) { >>> + swp_entry_t swp_entry; >>> >>> dec_mm_counter(vma->vm_mm, MM_SWAPENTS); >>> - pteval = swp_entry_to_pte(make_swapin_error_entry()); >>> - set_pte_at(vma->vm_mm, addr, pte, pteval); >>> - swap_free(entry); >>> + if (hwposioned) { >>> + swp_entry = make_hwpoison_entry(swapcache); >>> + page = swapcache; >> >> This might work for the process accessing to the broken page, but ksm >> pages are likely to be shared by multiple processes, so it would be >> much nicer if you can convert all mapping entries for the error ksm page >> into hwpoisoned ones. Maybe in this thorough approach, >> hwpoison_user_mappings() is updated to call try_to_unmap() for ksm pages. >> But it's not necessary to do this together with applying mcsafe-memcpy, >> because recovery action and mcsafe-memcpy can be done independently. >> > > I'm afraid leaving the ksm page in the cache will repeatedly trigger uncorrectable error for the > same page if ksm pages are shared by multiple processes. This might reach the hardware threshold > and result in fatal uncorrectable error (thus casuing system to panic). So IMHO it might be better > to check if page is hwpoisoned before calling ksm_might_need_to_copy() if above thorough approach > is not implemented. But I can easily be wrong. > Oh，missing this one，there are only two caller, one in do_swap_page(), it has already check whether the page is hwpoisoned or not, another is in unuse_pte() which only called from swapoff, it is not a hot patch, so I don't think it is an urgent requirement. Thanks.