From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0668A33E37A for ; Tue, 25 Aug 2026 16:43:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676200; cv=none; b=dPl+jTc5TPHVFFb7UBvU31HqpyDbjsWOFVN7ZugBzzguGGjtJ68Tg1Ax+2GYxmGeegPD3K74AsZS2IJ+dX3Nz/+zLvg27j5ZzfjfYQ5d2JTNbhgtm18r0BtfqImB5VXRAXmS399mGlGAJIrf8Xz83SfIwMaMxWjP9aaMZ56bymc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676200; c=relaxed/simple; bh=33tHj73w72eZPMblGfo+XiZ5GGd/wcICKIp2YnOVA+c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=roXu9Uh0xg7zUOt5EXI+xFVzNpp1KtRhQWtSwOgdlMZI5Vk+SJ6R9uIyn4rS5Vod+xHsmz1Q4aLxMRVzPtCw1h5FAXP1S3i9WHYvVYjgbYzLnsfdhQZrz1gTya5N0TmNSuhSQksj50m7o8J3D++KKLxczCxqTBjenHutevr6+RE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IE3OuFBy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IE3OuFBy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5FA661F00A3D; Tue, 25 Aug 2026 16:43:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787676198; bh=/pK8vkfuWdkoNNlq7Hv6MaryEnIssRFRjSinEh1fnZI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=IE3OuFByNrywPpaGGkAeTYuowkSe/Uyx4GTBLLvHItS69MMaL0udgEh+uTYBriCUl 2pzC6FQK2CSyf/RMYIA7tdEe5lzNvIS96jBMMLKxulAc3k4VyLzXvRKLI78623AHhx wPzZWGNqV+gSQLn21/2iIzldBbqxtIAx1ehJpv736n5nN4Q38Ns7uuDEs9o/hmJLRB YCPWko2xdqNefcsnbGgbU0RgoVcJ2PirfbvjXpjwljsacFtloniVCvMR4gQiq7z2+N W8keyM7LqMZwAijoy/Rw4GEI99T2CK8IHwXTC38Vd0JILw1rLl6RGTCHunun7Lham9 2uQcrSfdLAmpw== Message-ID: <1e04196a-7079-4a8d-a1b7-844e60d08728@kernel.org> Date: Tue, 25 Aug 2026 18:43:09 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 3/3] x86/mm: add set_direct_map_ro_noflush() To: Dave Hansen , Xueyuan Chen , akpm@linux-foundation.org Cc: ljs@kernel.org, usama.arif@linux.dev, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, rppt@kernel.org, ryan.roberts@arm.com, ziy@nvidia.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lance Yang References: <20260730090647.2401252-1-xueyuan.chen21@gmail.com> <20260730090647.2401252-4-xueyuan.chen21@gmail.com> <2931f8a6-3780-4d6a-b19d-61cbbdad1a3a@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/25/26 18:18, Dave Hansen wrote: > On 7/30/26 02:06, Xueyuan Chen wrote: >> +int set_direct_map_ro_noflush(const void *addr, unsigned long nr_pages) >> +{ >> + unsigned long tempaddr = (unsigned long)addr; >> + struct cpa_data cpa = { >> + .vaddr = &tempaddr, >> + .pgd = NULL, >> + .numpages = nr_pages, >> + .mask_set = __pgprot(0), >> + .mask_clr = __pgprot(_PAGE_RW | _PAGE_DIRTY), >> + .flags = CPA_NO_CHECK_ALIAS, >> + }; >> + >> + return __change_page_attr_set_clr(&cpa, 1); >> +} > > A couple of concerns here. > > First, why the "_noflush"? Sure, the "this is a best effort hardening" > function argument can be made, so it doesn't need to be correct. But the > result is a function that's called once and also has some sharp corners > and relatively high potential for misuse. Let's just do the flush. > > Second, I see that the other set_direct_map*() callers use > CPA_NO_CHECK_ALIAS. The reasoning behind it dates back to 2008 and I'm > not 100% sure what it is referring to. On one hand, it would be nice to > have all the set_direct_map*() callers be consistent. On the other hand, > there shouldn't *be* any aliases of a 2M page that came out of the page > allocator. We almost want a CPA_ASSERT_NO_ALIASES that goes out and > checks for aliases more than we want to ignore them. (Note: I don't > expect you to fix this, but a simple comment saying that no aliases are > expected would be nice) > > Third, what's with the 'tempaddr'? Are you working around the 'const'? > Honestly, I'd rather have no const than have it and subvert it with > casting trickery. > > Last: > > int set_direct_map_invalid_noflush(struct page *page) > int set_direct_map_default_noflush(struct page *page) > int set_direct_map_valid_noflush(struct page *page, unsigned nr, ... > int set_direct_map_ro_noflush(const void *addr, unsigned long nr_pages) > > Which one of these things is not like the other, despite being named > just like them? > That's called out in the cover letter: " This series adds set_direct_map_ro_noflush() so mm code can make a direct-map range read-only, then uses it for the persistent huge zero folio. The helper is direct-map specific, takes an address-based range as discussed for set_direct_map* helpers[2], and leaves TLB invalidation to the caller. " and patch #1 " Use an address-based signature to match ongoing direct-map helper work[2], where existing page-based helpers may move the same way. The helper is direct-map specific and leaves TLB invalidation to its caller. Architectures without direct-map permission support keep existing behavior through the generic stub. " Currently it looks like this series would go in first, though, so it would be better to keep the existing style. -- Cheers, David