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 33EBDFCC9B2 for ; Tue, 10 Mar 2026 03:32:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7E7456B008C; Mon, 9 Mar 2026 23:32:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 76B2D6B0093; Mon, 9 Mar 2026 23:32:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 66DA36B0095; Mon, 9 Mar 2026 23:32:37 -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 55DB86B008C for ; Mon, 9 Mar 2026 23:32:37 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id E3F561C437 for ; Tue, 10 Mar 2026 03:32:36 +0000 (UTC) X-FDA: 84528731112.19.7126AEF Received: from canpmsgout02.his.huawei.com (canpmsgout02.his.huawei.com [113.46.200.217]) by imf27.hostedemail.com (Postfix) with ESMTP id 0AE544000D for ; Tue, 10 Mar 2026 03:32:32 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=huawei.com header.s=dkim header.b=25WpgtJU; spf=pass (imf27.hostedemail.com: domain of yintirui@huawei.com designates 113.46.200.217 as permitted sender) smtp.mailfrom=yintirui@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1773113553; 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=ukfr+AuSSjalhcEuGd775EwrTPxyhTtDQGkfF9cnnoI=; b=KQIuYjuOK8/W9p4TBY2aFT+ogBnTviFhvzRMI8m55MeWRkeefowqXbIzxM0LHB4MuMNvSO j3VyyhgIy9JIb5KrLZ8Psr/Gi4Ks6uaaw2Ta0OqN9BAumn5zusxvHPVt3NZhfig2pqNdw5 1PaJoNsLVBkUpYwxMWROGG6AlBelaVs= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=huawei.com header.s=dkim header.b=25WpgtJU; spf=pass (imf27.hostedemail.com: domain of yintirui@huawei.com designates 113.46.200.217 as permitted sender) smtp.mailfrom=yintirui@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773113553; a=rsa-sha256; cv=none; b=6PbdqTZhw8W8+nad6MEjOZqftql05sZpatCcqXNvZuojKwqyBgawwrBEXopZAYtSeow892 k8xFYUHiPN1BM3t5su19vwvxFz2DFGZW50XlO49yKpuKKl4R9W5FxTY9grNWhREGRESojz 6Z8wYGBK9V/g4Zf4dpkXVmVx8xGVhBM= dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=ukfr+AuSSjalhcEuGd775EwrTPxyhTtDQGkfF9cnnoI=; b=25WpgtJUdMU4EPFULH4K6br31HYc+68SzizJgcjOO0/WwTWrFm0I23gaAhtwXnemVVXog/D/6 BKz/296PrNYryXCSs7MiOe69iLEyRVgoaq5Khg5lETGv3V86EtVXKGw/JnmgCWQ0KZKoJSPlifM iFUEDnQb9cUjb9lEiLhCOWk= Received: from mail.maildlp.com (unknown [172.19.162.223]) by canpmsgout02.his.huawei.com (SkyGuard) with ESMTPS id 4fVK7D71ZgzcbS0; Tue, 10 Mar 2026 11:27:04 +0800 (CST) Received: from kwepemr500001.china.huawei.com (unknown [7.202.194.229]) by mail.maildlp.com (Postfix) with ESMTPS id 0A90840569; Tue, 10 Mar 2026 11:32:29 +0800 (CST) Received: from [10.174.179.248] (10.174.179.248) by kwepemr500001.china.huawei.com (7.202.194.229) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 10 Mar 2026 11:32:26 +0800 Message-ID: <875a5d1b-4bed-4f70-a122-acd625265bfa@huawei.com> Date: Tue, 10 Mar 2026 11:32:26 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v3 2/4] mm/pgtable: Make pfn_pte() filter out huge page attributes To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , Matthew Wilcox CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Kefeng Wang , References: <20260228070906.1418911-1-yintirui@huawei.com> <20260228070906.1418911-3-yintirui@huawei.com> <5eaf3846-01db-471e-9903-b0b239d7838d@suse.com> <4d7c396a-6a48-4e56-b8d1-3ac7bd5d10fb@suse.com> From: Yin Tirui In-Reply-To: <4d7c396a-6a48-4e56-b8d1-3ac7bd5d10fb@suse.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.179.248] X-ClientProxiedBy: kwepems100001.china.huawei.com (7.221.188.238) To kwepemr500001.china.huawei.com (7.202.194.229) X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 0AE544000D X-Stat-Signature: g19u4hzjijpgbcpmrwzgj4ngcancgn3q X-Rspam-User: X-HE-Tag: 1773113552-240755 X-HE-Meta: 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 2zpZJ74P YJOjD9TYbVSnCTT+MeVPPUj9myiMbJt8RLeyYepwwm3jVxSg8+yrjv6vnb+O+VN8jIlD2W2iglRIzuv9K2eWX46Cww7SbJ7mb6sxy4LYbJWuqPZsnbBhcf2RBjqexbLOfXnpzsr1gWjKJ9ZpeZmD9pfzDA5Sl37+nLbvF62C7KfmiNLwGVPFEEAy5ZNj501DDGn/b8nkh7Z49GNiCBtVEOBDB/gF+ub0iTGmM+dGcD/RjTzqRBWuTbUZ4WW5nfgZ4f18sV8PXHfyck9oCVeX1qqrBwt0XheSe60WlW4z4azSSrL8lzSHG1i9a+A6cNVzQH2xTBzz+PIFnqXiSOFjdAxdcxx8l3ExDiajRSFdnXseW9UZxd5E5a7v18BLENqxYe7xBTw1Jp6RcSQk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/5/2026 6:05 PM, Jürgen Groß wrote: >> Hi Willy and Jürgen, >> >> Following up on the x86 _PAGE_PSE and _PAGE_PAT aliasing issue. >> >> To achieve the goal of keeping pfn_pte() pure and completely >> eradicating the pte_clrhuge() anti-pattern, we need a way to ensure >> pfn_pte() never receives a pgprot with the huge bit set. >> >> @Jürgen: >> Just to be absolutely certain: is there any safe way to filter out the >> huge page attributes directly inside x86's pfn_pte() without breaking >> PAT? Or does the hardware bit-aliasing make this strictly impossible >> at the pfn_pte() level? > > There is no huge bit at the PTE level. It is existing only at the PMD > and the > PUD level. > > So: yes, it is absolutely impossible to filter it out, as the bit has a > different meaning in "real" PTEs (with "PTE" having the meaning: a > translation > entry in a page referenced by a PMD entry not having the PSE bit set). > Hi Jürgen, Thank you for your confirmation. >> >> @Willy @Jürgen: >> Assuming it is impossible to filter this safely inside pfn_pte() on >> x86, we must translate the pgprot before passing it down. To maintain >> strict type-safety and still drop pte_clrhuge(), I plan to introduce >> two arch-neutral wrappers: >> >> x86: >> /* Translates large prot to 4K. Shifts PAT back to bit 7, inherently >> clearing _PAGE_PSE */ >> #define pgprot_huge_to_pte(prot)    pgprot_large_2_4k(prot) >> /* Translates 4K prot to large. Shifts PAT to bit 12, strictly sets >> _PAGE_PSE */ >> #define pgprot_pte_to_huge(prot) >> __pgprot(pgprot_val(pgprot_4k_2_large(prot)) | _PAGE_PSE) > > Seems to be okay. While the wrapper approach handles the aliasing, Willy recently suggested taking it a step further by embedding this translation directly into `pfn_pmd()` and `pmd_pgprot()`. I am going to explore this embedded approach for the v4 respin. -- Yin Tirui