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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 70F8DCD8C9D for ; Mon, 8 Jun 2026 10:40:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C34BB6B0092; Mon, 8 Jun 2026 06:40:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BBECC6B0093; Mon, 8 Jun 2026 06:40:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A86526B0095; Mon, 8 Jun 2026 06:40:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 924C46B0092 for ; Mon, 8 Jun 2026 06:40:05 -0400 (EDT) Received: from smtpin27.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 2C439C33BE for ; Mon, 8 Jun 2026 10:40:05 +0000 (UTC) X-FDA: 84856400370.27.0C7FBFC Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf25.hostedemail.com (Postfix) with ESMTP id 7EB0CA000D for ; Mon, 8 Jun 2026 10:40:03 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=dRZ35HRM; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf25.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780915203; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=UAI22XDH8Rk02hdvoTH5Zr8kOOXybFt3zj/PmpT+vR0=; b=OInlRgIy2n2opDWN0J5GHtV/jPuJtJXJzo7FObLfi+Ri3Aj3V+MCHaJ+g6qV3tjC7Xm8TO a7H4wb9q40DjOHKAGuP8QOCGn5o4I/ENw1+IPL+3mE0DEfsuiwZrBMoO4gSvOaiGTJa6nu qlEHCs2GbmZH4v9X9fJyU1qsdyE0UGg= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=dRZ35HRM; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf25.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780915203; b=C6ifvwWnktt8ZXtT5bL1VTUehChdUG3Am2UnBIXOBjeAZwvmZk7pHXzm/CvFjar1Jcr1nb PjLKuHlWBchXcK3bA/1aUw9nfEgkHl2D+SkhXO+mBpJ3HQAk/k4i5ibKE1Uvafy9FcLlI8 05Xavt9r0rcZt4Xgn8uALJTHH4xjArM= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 8E70444276; Mon, 8 Jun 2026 10:40:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA8131F00893; Mon, 8 Jun 2026 10:39:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780915202; bh=UAI22XDH8Rk02hdvoTH5Zr8kOOXybFt3zj/PmpT+vR0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=dRZ35HRMCB5YSX2evh0CzhDac0sfa/9kUKcQbFlfBcNsqTjaHSKDIzFE6dOYCqSOR BUqJZ+XA9CN8FBP52TGvSNdRnFmOPGzJnBdBc7oufRxFlAre4qCxSYKXJMB48tPDCg +ocEPqSN9xwVrfWctPMv3Rr7rUsD06LgHJGhlhL6pRHwiNyrhwZIn/W8UTd2dW3rX1 XqHgCqrrgeiEu2HyAZG17AKzc4n0mZN/ICwW0yAnunJFvWxXe4EprolwzVzG5V2uol /K4Qfq2c8SFn65Y15w92rlVyjpdUDrBvbDnlmzxRCpeVADi7bn0EXdCDRIj3W771IA ZsoN//T+zOjXA== Date: Mon, 8 Jun 2026 11:39:49 +0100 From: Lorenzo Stoakes To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Muchun Song , Oscar Salvador , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli Subject: Re: [PATCH v10 13/37] mm: use __GFP_ZERO in vma_alloc_zeroed_movable_folio Message-ID: References: <862a59e98104db76ee3998460bfc55e937c218c4.1780906288.git.mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <862a59e98104db76ee3998460bfc55e937c218c4.1780906288.git.mst@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 7EB0CA000D X-Stat-Signature: 57zmb69zb8ek6brxk4dymuy8oabb4fgr X-HE-Tag: 1780915203-751065 X-HE-Meta: U2FsdGVkX19DIEmavd63Ztu7ukLOoOI87SYreBzZeHtUovsXeDyt4XZam0s6Hml9U6VuxKcIkdvWtxiu81E4yJHT+SsBUSOC5S+dh+fzOTJaZ8bLf3Ue+nEJun94SWn3UAZ417sjAf24UyLAWlRGnAL0sGICsfmRaxTpTtleCKJz5I2GWhatBk8KxxStDF2opXzRevb8Lqxv7fYEVNpZehlsiF8sLXyT/aSwiGT7d2WnOz+M+By7tc3+9DlWuQfiaR1omod4SRXZ7XMbUWmOzNEJahU+SjJxCKt9c9Il4pDiDalMfnacMQML/QvqNWmQOnPmFSzskb0GvK4aG77UqtrJ5HxKEYpMP+ZHY80KpZ2Fwkax+0XGZcKCRsGG+KPSFW61ER5x1ejldeO8TDNkwTgu35BeemPtv1/NmMFa/saOvSxpMx9NKYhsGnXtkTNa7jwWoJrow+rY6vf6pE6YncdY4N78Ap7gU+3P1AfNHTyrku1pLd6qzZ3TUTaboe6ibufor4o8juq7Q4nBDRweS5Bin9sTVCSgafNEMr6BvwoexpKe55QgaYpTW8TAlHlWcsflwvFVncoCvWIZDlT6koTIcK2hxRiLWYnuDQ+mWftX5WPUWAqzSBDoOZNNDQfEt6dKiEpgbRXGxDmKRHippNorlbPcsBgLAjW5CqRIlikXBUyi00eaY+WT60lKaXl7N0vbpahZG9NQ54948BH6KAdQNb6s6nkKiZfWB0TP7kd/I45c82UPEsWXD0+VmWt+CM3axMZLhFMCuCGkQ1+VJGbbXcPDuIQz3nVVYmnLiZUYrc6QLfOJzxc/NzJy7BXY3X8WNjtIdJ5/D8j1Q8Pri+VFdEGSaPIGYvRo0wSeu5aexvLkyQt+ZicQMAfu7cSnt3bVNVWE184nJgRUO1Pu5VRioWLP3Yp2Zun2Mx87Yd7PHCmiI+HK+BRpmtmkF672un+VPYPi2STKUBmdUh5 lbx0YDMp claeB9c15tpDOrEo31Rob9BFdvNzZPrG3MeXGyItdn1DDG+XSVakvNXZbIUjBlRtTx+AxSwq2HDqQQ1Nm8TT2iSlL/zD9y2iGuuTyl+LKQvtZJbJThfCx8XzB9Jq1MZsTqMrsF8hgMiCWIG0tqDHz1HbTBtrFNOqZXAoa2+sjylSS+mnSkOd4+kIOkYncxLtIKJE5ZbBXa9wDL8tfgMyCrw42/Vnk8gt/r4T1XdKnjL5X3mlwBH6rKDC8BZSDi52sTDWlJ67HTz3WiVMoE27dMYtRp7dQyuj72hyQ3LMIg2GYLCybO+ewf3Pck9qtxBffk8lRvzXm5ng7F+iQrSbfe0mJVEqLGeP2TKR3gz4BWSdtuK8i7/d38gi4CVZv1bujOawZ66oobiWa8LzppHDPp/SWgw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 08, 2026 at 04:36:51AM -0400, Michael S. Tsirkin wrote: > Now that post_alloc_hook() handles cache-friendly user page > zeroing via folio_zero_user(), convert vma_alloc_zeroed_movable_folio() > to pass __GFP_ZERO instead of zeroing at the callsite. > > Note: before this series, replacing clear_user_highpage() with > __GFP_ZERO was unsafe on cache-aliasing architectures because > __GFP_ZERO uses clear_page() without a dcache flush. With this > series, it is safe if the caller passes a valid user address > (not USER_ADDR_NONE) to vma_alloc_folio() etc., which delivers Wait, so now you're making actual correctness predicated on correctly passing the right user address?? > it to post_alloc_hook() for the dcache flush via > folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed. Yeah, ok I'm beating a dead horse a bit here, but no to this approach. > > Signed-off-by: Michael S. Tsirkin > Assisted-by: Claude:claude-opus-4-6 > --- > include/linux/highmem.h | 9 ++------- > 1 file changed, 2 insertions(+), 7 deletions(-) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index d7aac9de1c8a..8b0afaabbc6e 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -320,13 +320,8 @@ static inline > struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma, > unsigned long vaddr) > { > - struct folio *folio; > - > - folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr); > - if (folio && user_alloc_needs_zeroing()) So now we are unconditionally zeroing the pages even if !user_alloc_needs_zeroing()? You don't mention this in the commit message and it seems like it'll regress performance? > - clear_user_highpage(&folio->page, vaddr); > - > - return folio; > + return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, > + 0, vma, vaddr); > } > #endif > > -- > MST > Thanks, Lorenzo