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X-CSE-ConnectionGUID: +HfgMjurSUylkkkb4Bm3yQ== X-CSE-MsgGUID: MiVkpNx+R7OuShf5zndiig== X-IronPort-AV: E=McAfee;i="6700,10204,11350"; a="40775914" X-IronPort-AV: E=Sophos;i="6.13,299,1732608000"; d="scan'208";a="40775914" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Feb 2025 13:33:37 -0800 X-CSE-ConnectionGUID: XXneleheS8aI0f46QupHtw== X-CSE-MsgGUID: /zLq0WsCR86gtLTRzeJITg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.13,299,1732608000"; d="scan'208";a="115370267" Received: from kinlongk-mobl1.amr.corp.intel.com (HELO [10.125.109.250]) ([10.125.109.250]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Feb 2025 12:53:45 -0800 Message-ID: <940c4972-fad0-4d61-a7ce-1c5d52891a5e@intel.com> Date: Wed, 19 Feb 2025 12:53:41 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/7] x86: Remove custom definition of mk_pte() To: "Matthew Wilcox (Oracle)" , linux-mm@kvack.org Cc: linux-arch@vger.kernel.org, x86@kernel.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org References: <20250217190836.435039-1-willy@infradead.org> <20250217190836.435039-5-willy@infradead.org> 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-Rspam-User: X-Rspamd-Queue-Id: F323140005 X-Rspamd-Server: rspam07 X-Stat-Signature: wuge3g4ro3my93mt3g7dtgbdznyczod3 X-HE-Tag: 1740000818-526148 X-HE-Meta: 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 i2JXfMfX 4QqWdPdx/+ILLWML37IMCa3D77xyyAF92fiuLZCX2cvyATTeYuO5+hqJYVlFuAcdPtgi6ZJ0k557FOkdOSPrl1k/E+Vg/Qu/Ri91ohqgTbrokTOFNpHRo5rgVSfDlJ7pYlZfdYkMkLGLcMU7xnMefOjkzBeV0JH4emo208iy8uECfAVX1tYzNgxJPiejuyBpZzcKhEkVQgQarp9dJKBRyvvN84MSSI6ltM0/rVikqYu/EDF7DKMPWUBBCbl9IAA7QEIibN6bTJZdONDg= 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 2/17/25 11:08, Matthew Wilcox (Oracle) wrote: > diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h > index 593f10aabd45..9f480bdafd20 100644 > --- a/arch/x86/include/asm/pgtable.h > +++ b/arch/x86/include/asm/pgtable.h > @@ -784,6 +784,9 @@ static inline pgprotval_t check_pgprot(pgprot_t pgprot) > static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot) > { > phys_addr_t pfn = (phys_addr_t)page_nr << PAGE_SHIFT; > + /* This bit combination is used to mark shadow stacks */ > + WARN_ON_ONCE((pgprot_val(pgprot) & (_PAGE_DIRTY | _PAGE_RW)) == > + _PAGE_DIRTY); Looks sane to me. Good riddance to unnecessary arch-specific code. Acked-by: Dave Hansen Just one note (in case anyone ever trips over that WARN_ON_ONCE()): This is a problem with the existing code and with your patch, but the 'pgprot' going to mk_pte() or pfn_pte() probably can't come from a hardware PTE that has the dirty bit clear. Old, pre-shadow-stack hardware could race between: 1. Software transitioning _PAGE_RW 1=>0 2. The CPU page walker trying to set _PAGE_DIRTY in response to a write and end up with a Write=0,Dirty=1 PTE. That doesn't happen for kernel memory because most or all of the PTEs that the kernel establishes have _PAGE_DIRTY=1 so the page walker never tries to set _PAGE_DIRTY. It's also generally some kind of a bug if one CPU is in the kernel trying to write to a page while another is making the page read-only. Anyway, I can basically see cases where this warning might trip, but it's very likely on older hardware when the kernel is doing something else silly.