From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D1A53101C5; Wed, 10 Apr 2024 08:16:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712736976; cv=none; b=eJQ8cHxoNcZMfVFY2bUM1gucXK91Rfa2Txb4xM4v1AcxQts42j2PBuorwaGz1gXqWSiA6kRXfcFSx32WThHmcTtc8XILUskyya0wySl205ppCcwOv2qycWGFVzSK4N6EbYKTsDHazWS3+caaHCPwSgalmEfgltdeL+b/wAZK/UA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712736976; c=relaxed/simple; bh=+BMKLZOsQbr0VOgMzU++BDRC6fIbczsfsXJLxYo5OFw=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=eS54BDt3UArSQ9IjaZntkon6PI0EqH6CkHF5YvYnLfFPVfHRlJJgsdbL+1avDXBUpDEWaWGu7e3u2hdCbQeQ5mQVYgwjOMO7lQxF90RBmeZlUxD0HBiGTQZHN+DrmP05BwtTSAjXnsHz8x9ckzckVnQPTTV0a3oekEdmJGbEK1o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.105]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4VDwYq151qzWmjq; Wed, 10 Apr 2024 16:13:03 +0800 (CST) Received: from canpemm500002.china.huawei.com (unknown [7.192.104.244]) by mail.maildlp.com (Postfix) with ESMTPS id 3EE1C14044F; Wed, 10 Apr 2024 16:16:11 +0800 (CST) Received: from [10.173.135.154] (10.173.135.154) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.35; Wed, 10 Apr 2024 16:16:10 +0800 Subject: Re: [PATCH] mm,swapops: Update check in is_pfn_swap_entry for hwpoison entries To: Oscar Salvador , Peter Xu CC: Andrew Morton , , , David Hildenbrand , , Tony Luck , Naoya Horiguchi References: <20240407130537.16977-1-osalvador@suse.de> From: Miaohe Lin Message-ID: <5b730a9c-440d-6527-a761-e15c9670af83@huawei.com> Date: Wed, 10 Apr 2024 16:16:10 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) On 2024/4/8 4:31, Oscar Salvador wrote: >> Totally unexpected, as this commit even removed hwpoison_entry_to_pfn(). >> Obviously even until now I assumed hwpoison is accounted as pfn swap entry >> but it's just missing.. >> >> Since this commit didn't really change is_pfn_swap_entry() itself, I was >> thinking maybe an older fix tag would apply, but then I noticed the old >> code indeed should work well even if hwpoison entry is missing. For >> example, it's a grey area on whether a hwpoisoned page should be accounted >> in smaps. So I think the Fixes tag is correct, and thanks for fixing this. >> >> Reviewed-by: Peter Xu > > Thanks Peter Thanks both. > >> Fedora stopped having DEBUG_VM for some time, but not sure about when it's >> still in the 6.1 trees. It looks like cc stable is still reasonable from >> that regard. > > Good to know, thanks for the info. > >> A side note is that when I'm looking at this, I went back and see why in >> some cases we need the pfn maintained for the poisoned, then I saw the only >> user is check_hwpoisoned_entry() who wants to do fast kills in some >> contexts and that includes a double check on the pfns in a poisoned entry. >> Then afaict this path is just too rarely used and buggy. > > Yes, unfortunately memory-failure code does not get exercised that much, > and so there might be subtly bugs lurking in there for quite some time. There're many memory-failure testcases but some code paths still didn't get exercised. That's a pity. :( > >> A few things we may need fixing, maybe someone in the loop would have time >> to have a look: >> >> - check_hwpoisoned_entry() >> - pte_none check is missing >> - all the rest swap types are missing (e.g., we want to kill the proc too >> if the page is during migration) Firstly, I thought rest swap types just won't exist in this code path. But after second thought, it seems it's possible. For example, when page is being isolated for migration, memory_failure will fails to isolate it. And the second MCE event will goes to kill_accessing_process() and see a migrate swap entry. >> - check_hwpoisoned_pmd_entry() >> - need similar care like above (pmd_none is covered not others) > > I will have a look and see what needs fixing, thanks for bringing it up. Thanks for your time. . > >