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X-CSE-ConnectionGUID: i1+wvCMnQoOJ4zbkEMmJnQ== X-CSE-MsgGUID: ZY3qJ3qcTv6ouIr5Ebhvnw== X-IronPort-AV: E=McAfee;i="6700,10204,11394"; a="62631346" X-IronPort-AV: E=Sophos;i="6.15,188,1739865600"; d="scan'208";a="62631346" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by orvoesa102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Apr 2025 09:43:04 -0700 X-CSE-ConnectionGUID: PNDCImh2SwmUq/OXMReN8A== X-CSE-MsgGUID: 2z30JdBbQJeAh01BitZsnQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.15,188,1739865600"; d="scan'208";a="127247176" Received: from daliomra-mobl3.amr.corp.intel.com (HELO [10.124.223.29]) ([10.124.223.29]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Apr 2025 09:42:57 -0700 Message-ID: <257b39a5-69bf-4e6d-844b-576e9c9d2e7d@intel.com> Date: Fri, 4 Apr 2025 09:42:55 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 05/14] x86: Reset tag for virtual to physical address conversions To: Maciej Wieczor-Retman , hpa@zytor.com, hch@infradead.org, nick.desaulniers+lkml@gmail.com, kuan-ying.lee@canonical.com, masahiroy@kernel.org, samuel.holland@sifive.com, mingo@redhat.com, corbet@lwn.net, ryabinin.a.a@gmail.com, guoweikang.kernel@gmail.com, jpoimboe@kernel.org, ardb@kernel.org, vincenzo.frascino@arm.com, glider@google.com, kirill.shutemov@linux.intel.com, apopple@nvidia.com, samitolvanen@google.com, kaleshsingh@google.com, jgross@suse.com, andreyknvl@gmail.com, scott@os.amperecomputing.com, tony.luck@intel.com, dvyukov@google.com, pasha.tatashin@soleen.com, ziy@nvidia.com, broonie@kernel.org, gatlin.newhouse@gmail.com, jackmanb@google.com, wangkefeng.wang@huawei.com, thiago.bauermann@linaro.org, tglx@linutronix.de, kees@kernel.org, akpm@linux-foundation.org, jason.andryuk@amd.com, snovitoll@gmail.com, xin@zytor.com, jan.kiszka@siemens.com, bp@alien8.de, rppt@kernel.org, peterz@infradead.org, pankaj.gupta@amd.com, thuth@redhat.com, andriy.shevchenko@linux.intel.com, joel.granados@kernel.org, kbingham@kernel.org, nicolas@fjasle.eu, mark.rutland@arm.com, surenb@google.com, catalin.marinas@arm.com, morbo@google.com, justinstitt@google.com, ubizjak@gmail.com, jhubbard@nvidia.com, urezki@gmail.com, dave.hansen@linux.intel.com, bhe@redhat.com, luto@kernel.org, baohua@kernel.org, nathan@kernel.org, will@kernel.org, brgerst@gmail.com Cc: llvm@lists.linux.dev, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, x86@kernel.org References: 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-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1401212000B X-Stat-Signature: 6eqnzzmyeytq99mqr43xkx88sg78moba X-Rspam-User: X-HE-Tag: 1743784985-162832 X-HE-Meta: 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 rVCnykVn mitrhergiDsTWne2gF8s9WuvAQmaxQCaBiYVoFMArQlJ8IviH2Up9jRbTu9RFvj8zcHbHH8ZnH/YyLjRSnMBCdYAvGv7z1UDubMN0aeKLXE0NkK5HMsChwL3Z11uzYW/aard8XhIki+dZzijl168BJENNDmq4IAmgoXTGdyDy2tabe5HZlAoEUc7W34Mcq6JhcKpCH1s6/QdvIQsSJ5O964ifI/Qst5dBqP8smKEvEMT9Dd0AuHTSw64dUSnKiaSrj6hXfqB0Y0GyFaiqgmArdpzm8Q== 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 4/4/25 06:14, Maciej Wieczor-Retman wrote: > +#ifdef CONFIG_KASAN_SW_TAGS > +#define page_to_virt(x) ({ \ > + __typeof__(x) __page = x; \ > + void *__addr = __va(page_to_pfn((__typeof__(x))__tag_reset(__page)) << PAGE_SHIFT); \ > + (void *)__tag_set((const void *)__addr, page_kasan_tag(__page)); \ > +}) > +#endif Is this #ifdef needed? I thought there were stub versions of all of those tag functions. So it should be harmless to use this page_to_virt() implementation with or without KASAN. Right? I'm also confused by the implementation. This is one reason why I rather dislike macros. Why does this act like the type of 'x' is variable? Isn't it always a 'struct page *'? If so, then why all of the __typeof__()'s? Are struct page pointers _ever_ tagged? If they are, then doesn't page_to_pfn() need to handle untagging as well? If they aren't, then there's no reason to __tag_reset() in here. What was the thinking behind this cast: (const void *)__addr ? Are any of these casts _doing_ anything? I'm struggling to find anything wrong with: #define page_to_virt(x) ({ void *__addr = __va(page_to_pfn(__page) << PAGE_SHIFT); __tag_set(__addr, page_kasan_tag(x)) }) ... which made me look back at: static inline const void *__tag_set(const void *addr, u8 tag) from patch 3. I don't think the 'const' makes any sense on the return value here. Surely the memory pointed at by a tagged pointer doesn't need to be const. Why should the tag setting function be returning a const pointer? I can see why it would *take* a const pointer since it's not modifying the memory, but I don't see why it is returning one.