From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB53AC3DA49 for ; Fri, 26 Jul 2024 11:56:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 010096B009E; Fri, 26 Jul 2024 07:56:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F01F46B00A0; Fri, 26 Jul 2024 07:56:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D54616B00A4; Fri, 26 Jul 2024 07:56:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id B89186B009E for ; Fri, 26 Jul 2024 07:56:55 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 723711C12DC for ; Fri, 26 Jul 2024 11:56:55 +0000 (UTC) X-FDA: 82381752390.20.6B2BB41 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf20.hostedemail.com (Postfix) with ESMTP id 57D751C001A for ; Fri, 26 Jul 2024 11:56:53 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=g+66Flo7; spf=pass (imf20.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1721994988; a=rsa-sha256; cv=none; b=1zdHPrhrAL76aDFr4nfzoKliSU2KgdgLo3p3kw+b36Rc8CQ1k6mo3M6xUg3H4KQ7b9szse oxRwLuyDm7NnRupwUZUNC++11CCaqUcj+XTGjKtuUn7cocoH0UzHDpXa/gOawr/GBbBnNj wFDa/Et2+lttMoJ+9vDTMgMqfOq9fvM= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=g+66Flo7; spf=pass (imf20.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1721994988; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=4Z86IH/NwuVbs4wh6Itna1eI4RVlRsUnJ2R+cQ/ZJjM=; b=x7YjGdZ8Zg2JSpBvY7NJkqcip47bgY0J3ClYdnFE0LdE5wkt7PwCVDVJtk1lm0hRaChDvF DlcROJKSnOFz8F77nE3qhcsUltTUgI9fMkvrXJUeD53d+raHPFHhOoJ/UPyyxh2YRTmsCG 13JLNDxuEMaLCgeLJuYgd5uhPD0ONsU= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1721995012; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4Z86IH/NwuVbs4wh6Itna1eI4RVlRsUnJ2R+cQ/ZJjM=; b=g+66Flo7xtMc8KGlUM19YvKEDkNAKyL4CIWItT/kpVWaHI58/YbxgBQcva14y0mpzpImNz 6uh9xhiB4M+7VNnjOBeBn2eBWE6XxlLnAxlnJudu16qR17wfznFxW0+hNslHqw/my5UQDq +TlgOZDPbi5Hd6WSLrzcV6fWMOR2ke4= Received: from mail-qv1-f70.google.com (mail-qv1-f70.google.com [209.85.219.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-552-O_LmjiBqOleLcCmg2ukKSQ-1; Fri, 26 Jul 2024 07:56:51 -0400 X-MC-Unique: O_LmjiBqOleLcCmg2ukKSQ-1 Received: by mail-qv1-f70.google.com with SMTP id 6a1803df08f44-6b7678caf7dso1964876d6.1 for ; Fri, 26 Jul 2024 04:56:51 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721995010; x=1722599810; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=4Z86IH/NwuVbs4wh6Itna1eI4RVlRsUnJ2R+cQ/ZJjM=; b=opiGYBtam52SdPE8UouyUAC+LSpkhkgC5Me7s9w/dxOvtaU/LeM5Yi8JibIkAa3lTO fbUOToD0W2GTly0hESLZwptHFXfKjGc278a8SgSEvmdnstvJPD89tkPwD/wXGInPH7DJ NR4SmJ1FSF1SFJKQ8pi5Z6P0Sx5paWq2VS2l3aNT99oaYQ9r4bQrvmBltnCABDCBfJ/x qLOWsSvDaCuZ5EoQDCY2qM9nQU/MKdK9F6N5umKVMui3icJ5eNpODQBkH4xSPl9iAuR3 f9JLRxs9xGYt4wXXPq2pdo7yQSKW/Yb1p1Ugwe+cHSe2kaka7amiA2XDOveaKR4Mi3+N 9ZBg== X-Gm-Message-State: AOJu0YxLu/a0cMDs6xxJUCRSWRudX0jQh++jMTCqf4wYmVekmhHxYo+t atQUdkTCAFL6rPrtoRlH/Tlelev6LvYKIb2X4DJoeQxhSmR9nHQdZf8NgZpDblfvvujsMdKn3h6 Ih/Rog0VFk0eRe3NIae1zIHv1u6t/pgvDc+KiLm31Bz7R0+II X-Received: by 2002:a05:6214:519a:b0:6b0:6370:28d4 with SMTP id 6a1803df08f44-6bb3e36d07bmr37225376d6.6.1721995010421; Fri, 26 Jul 2024 04:56:50 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEEGvC2s1YpmC7Xh0oPNbR2PTMgHDtIWIWACRSqNjlE8cYjZEpmS07NBeANfwhQ2eLo+N025Q== X-Received: by 2002:a05:6214:519a:b0:6b0:6370:28d4 with SMTP id 6a1803df08f44-6bb3e36d07bmr37225126d6.6.1721995009990; Fri, 26 Jul 2024 04:56:49 -0700 (PDT) Received: from x1n (pool-99-254-121-117.cpe.net.cable.rogers.com. [99.254.121.117]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6bb3fb17327sm15684346d6.145.2024.07.26.04.56.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jul 2024 04:56:49 -0700 (PDT) Date: Fri, 26 Jul 2024 07:56:46 -0400 From: Peter Xu To: James Houghton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Jiang , Rik van Riel , Dave Hansen , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Matthew Wilcox , Rick P Edgecombe , Oscar Salvador , Mel Gorman , Andrew Morton , Borislav Petkov , Christophe Leroy , Huang Ying , "Kirill A . Shutemov" , "Aneesh Kumar K . V" , Dan Williams , Thomas Gleixner , Hugh Dickins , x86@kernel.org, Nicholas Piggin , Vlastimil Babka , Ingo Molnar Subject: Re: [PATCH v3 8/8] mm/mprotect: fix dax pud handlings Message-ID: References: <20240715192142.3241557-1-peterx@redhat.com> <20240715192142.3241557-9-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Stat-Signature: ea6gw8gpzfmekw1ghirxopm1r76trg4p X-Rspamd-Queue-Id: 57D751C001A X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1721995013-337293 X-HE-Meta: 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 ufAL3Zfd jcW3TIGTHp8OwI7fvEoYTKNwS8epJBOnBMv5TtDIqJVAZN/oGOSzBbznKP022Fk8NgV345nf69iCX9NCCIgrmVy4PSPSFk8/o3c/6p3QbrchsD1Kh3WAdX0qV3njHc8O/3DYC2p9HViA5WDkP/pJamsv3Pkopc/LKrc7mldSgTC+KtpyF2zdSNvtg0fyhqkDPwKzjBl+Yn71sazJxvKllEDaEwh44aO6whF1/Q6Ha6XYH+jdxgGwd1W2uOJIG4AeC37V3TbO4HYCE9px3uITK51LOXewHKhTncI2SWDMYoUOM6OUujPvPvX/GgsmQd39XI/kss5lql6/C5WMU9vxmKZlFhmv/krDFt1AdVTC/FHlrmQt7S4ZwhwbC6iorzDflW9h2t4KsFB2DebgeZnJLvgWfZbCFJBjpNzjuoXvB8VjI3Gf9/kHJ1gCgUhNDqZIH9RCYY/qwbd3KqVsM3M1PjP7NDyRWBUghmFZeVnwx2Kto/R4= 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: List-Subscribe: List-Unsubscribe: On Thu, Jul 25, 2024 at 05:23:48PM -0700, James Houghton wrote: > On Thu, Jul 25, 2024 at 3:41 PM Peter Xu wrote: > > > > On Thu, Jul 25, 2024 at 11:29:49AM -0700, James Houghton wrote: > > > > - pages += change_pmd_range(tlb, vma, pud, addr, next, newprot, > > > > + > > > > + if (pud_leaf(pud)) { > > > > + if ((next - addr != PUD_SIZE) || > > > > + pgtable_split_needed(vma, cp_flags)) { > > > > + __split_huge_pud(vma, pudp, addr); > > > > + goto again; > > > > > > IIUC, most of the time, we're just going to end up clearing the PUD in > > > this case. __split_huge_pud() will just clear it, then we goto again > > > and `continue` to the next pudp. Is that ok? > > > > > > (I think it's ok as long as: you never map an anonymous page with a > > > PUD, > > > > I think this is true. > > > > > and that uffd-wp is not usable with non-hugetlb PUD mappings of > > > user memory (which I think is only DAX?). > > > > Uffd-wp has the async mode that can even work with dax puds.. even though I > > don't think anyone should be using it. Just like I'm more sure that nobody > > is using mprotect() too with dax pud, and it further justifies why nobody > > cared this much.. > > > > What uffd-wp would do in this case is it'll make pgtable_split_needed() > > returns true on this PUD, the PUD got wiped out, goto again, then > > change_prepare() will populate this pud with a pgtable page. Then it goes > > downwards, install PMD pgtable, then probably start installing pte markers > > ultimately if it's a wr-protect operation. > > Ah, I didn't understand this patch correctly. You're right, you'll > install PMDs underneath -- I thought we'd just find pud_none() and > bail out. So this all makes sense, thanks! > > > > > > So it seems ok today...?) > > > > Yes I think it's ok so far, unless you think it's not. :) > > > > > > > > Also, does the comment in pgtable_split_needed() need updating? > > > > /* > > * Return true if we want to split THPs into PTE mappings in change > > * protection procedure, false otherwise. > > */ > > > > It looks to me it's ok for now to me? THP can represents PUD in dax, and we > > indeed want to break THPs (no matter PUD/PMD) finally into PTE mappings. > > Oh, heh I was thinking of the other comment: > > /* > * pte markers only resides in pte level, if we need pte markers, > * we need to split. We cannot wr-protect shmem thp because file > * thp is handled differently when split by erasing the pmd so far. > */ > > I guess this is fine too, it just kind of reads as if this function is > only called for PMDs. *shrug* Ah ok, yeah it looks mostly fine here too. Let's make this easy by keeping it as-is, but if there'll be a new version I can touch it up if it helps the readings. > > > > > > > > > Somewhat related question: change_huge_pmd() is very careful not to > > > clear the PMD before writing the new value. Yet change_pmd_range(), > > > when it calls into __split_huge_pmd(), will totally clear the PMD and > > > then populate the PTEs underneath (in some cases at least), seemingly > > > reintroducing the MADV_DONTNEED concern. But your PUD version, because > > > it never re-populates the PUD (or PMDs/PTEs underneath) does not have > > > this issue. WDYT? > > I guess I'm wrong about this -- your PUD version is the same as the > PMD version in this respect: both clear the PUD/PMD and then install > lower page table entries. > > > > > Could you elaborate more on the DONTNEED issue you're mentioning here? > > In change_huge_pmd(), there is a comment about not clearing the pmd > before setting the new value. I guess the issue is: if a user is > MADV_DONTNEEDing some memory and happens to see a cleared PMD, it will > just move on. But in this case, if change_huge_pmd() temporarily > cleared a PMD, then MADV_DONTNEED saw it and moved on, and then > change_huge_pmd() installed a new PMD, the MADV_DONTNEED has basically > skipped over the PMD, probably not what the user wanted. It seems like > we have the same issue when a PMD is cleared when we're splitting it. > > But yeah, given that your PUD version is apparently no different from > the PMD version in this respect, maybe this question isn't very > interesting. :) Ah that one, so yeah that's why I introduced pudp_invalidate() in this series to make sure that issue isn't there. Then I assume we're good. Thanks, -- Peter Xu