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X-CSE-ConnectionGUID: M8CNG2m5T2SPUroedOYtIA== X-CSE-MsgGUID: 5p1zDt7ITCCw3KYqebojzA== X-IronPort-AV: E=McAfee;i="6800,10657,11886"; a="75683614" X-IronPort-AV: E=Sophos;i="6.25,243,1779174000"; d="scan'208";a="75683614" Received: from fmviesa008.fm.intel.com ([10.60.135.148]) by fmvoesa110.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Aug 2026 09:18:02 -0700 X-CSE-ConnectionGUID: IVmEJ8cGTRWmBQlOpXyt3g== X-CSE-MsgGUID: cI6+c/a6RCu4ERA2CPiKxQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,243,1779174000"; d="scan'208";a="264708705" Received: from aschende-mobl.amr.corp.intel.com (HELO [10.125.109.12]) ([10.125.109.12]) by fmviesa008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Aug 2026 09:18:02 -0700 Message-ID: <2931f8a6-3780-4d6a-b19d-61cbbdad1a3a@intel.com> Date: Tue, 25 Aug 2026 09:18:01 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 3/3] x86/mm: add set_direct_map_ro_noflush() To: Xueyuan Chen , akpm@linux-foundation.org Cc: david@kernel.org, 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> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: kpa71pwkkppf3x6yjrgz3ftw1jmfph3s X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C61D61C0005 X-Rspam-User: X-HE-Tag: 1787674683-572510 X-HE-Meta: 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 PAYD4qUt U927YOK1NJtgTtO8KC5AoWi2OCU12mq6ikttcLP8TvkLKTZIfzp6QTGnyfGrQDW40hTbqD6QNdN9vTnesf0VqE5UmzNXrhPbJF75b5bBKmS3G5R4PTnwN3SrNHOvEYDoy9/qCnUpS3r0/CqeJupUiL6OaoTqNhN/jWL9gPVSVJKfIIflikKLWiDC+gRtY6/F9v1GG2OFurKwhhp6wiAGHwRQg6koXIS+5H3ypDQo0h3W98Q638ss3Hxvy40hNTXbrsbvXBC9xIisOpQIZ7zx6D1H7clumwniPrSbBX2pbPMseBcJFH9z7qkuclzbl6sjdLW+FBVwXvBSBKhk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? Imagine the fun if someone did: set_direct_map_ro_noflush(page, 1); and set_direct_map_default_noflush(page)