From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AIpwx4+yvxEzQREeETusZyqgTw78MKv8ygWhcgj+uP5G+H/VJyBkPpStLKpjvMWmdTpZlh3QIPdN ARC-Seal: i=1; a=rsa-sha256; t=1523517401; cv=none; d=google.com; s=arc-20160816; b=b6wKzw/NLQRuEgLpkcs4k0sRBDTC7scKHdXKo0/zl6yJmkO/YLUhDa/C3qytqwNylM Whhm5DVCPeVdNkhM0OVshoOORSIhdTDZwiJ2w7NM1bumjfNtgPt8UNV8tsF6SzOkarty dXGRz5vywu0A2mjPcvXyWUD/4spDz2J+ImqSVqKUZFdBopu2+wOJsIASJx/FZkhkQhCL A1Iql8a9e7NpmIcFtttZZ1SR6yDMXnXHwXgxfPFL60ekXZ4J6tJoNIw1Slq3Y0EFhfPy s5oEKuRlf8dzCykKmmbVaTuzo5jBgPLxQnLp9Df1Shj/rcBlzXdMkR5+Xf0BkUhr90ce sIjg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=precedence:content-disposition:content-transfer-encoding :mime-version:robot-unsubscribe:robot-id:git-commit-id:subject:to :references:in-reply-to:reply-to:cc:message-id:from:sender:date :arc-authentication-results; bh=AR6oQaOFZtzU4VAsi+2Uau9tRcWlKFMlKObeEmaEYNo=; b=cj00ve38iqh/xuqgBy0vL5iWJbC4IfUeiTKp4DTDPxR2J1xMn0wJhP5v8RGsVtmMl8 jrjctEqd/EuREs6QCyBDnSIQ8BUmnZ2hJ4ECExuFXCVexvY3/WGCwqvUpuSXJPBSDK9J uJ0lTQrJUhz6/b93hvQNbO78gedH1CjnHoZ1bnjq3T3Wf8eHvZxwrbzzkK2UXVQVnpYL NGUCkaetJEYWjnrlB5qXybTvRl7wRTEqbbni5BU97+z3F5yRBtS+mxdu4eDVlIDBjo08 XNdolFvDWkpVq8GynJnUQPdT7zA+J7rTxZ3fK+WITwjXNvNg9jpApoIFTH5ePRoC7ZqJ 1yRg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of tipbot@zytor.com designates 198.137.202.136 as permitted sender) smtp.mailfrom=tipbot@zytor.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of tipbot@zytor.com designates 198.137.202.136 as permitted sender) smtp.mailfrom=tipbot@zytor.com Date: Thu, 12 Apr 2018 00:14:58 -0700 Sender: tip tree robot From: tip-bot for Dave Hansen Message-ID: Cc: luto@kernel.org, dave.hansen@linux.intel.com, keescook@google.com, dan.j.williams@intel.com, torvalds@linux-foundation.org, mingo@kernel.org, jgross@suse.com, dwmw2@infradead.org, hughd@google.com, gregkh@linuxfoundation.org, peterz@infradead.org, hpa@zytor.com, namit@vmware.com, arjan@linux.intel.com, tglx@linutronix.de, jpoimboe@redhat.com, aarcange@redhat.com, linux-kernel@vger.kernel.org, bp@alien8.de Reply-To: dwmw2@infradead.org, jgross@suse.com, hughd@google.com, gregkh@linuxfoundation.org, peterz@infradead.org, hpa@zytor.com, namit@vmware.com, luto@kernel.org, dave.hansen@linux.intel.com, keescook@google.com, mingo@kernel.org, torvalds@linux-foundation.org, dan.j.williams@intel.com, aarcange@redhat.com, linux-kernel@vger.kernel.org, bp@alien8.de, tglx@linutronix.de, arjan@linux.intel.com, jpoimboe@redhat.com In-Reply-To: <20180406205513.079BB265@viggo.jf.intel.com> References: <20180406205513.079BB265@viggo.jf.intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/pti] x86/mm: Comment _PAGE_GLOBAL mystery Git-Commit-ID: 430d4005b8b41c19966dd3bfdb33004bdb2de01c X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1597289661093401125?= X-GMAIL-MSGID: =?utf-8?q?1597523782441333090?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Commit-ID: 430d4005b8b41c19966dd3bfdb33004bdb2de01c Gitweb: https://git.kernel.org/tip/430d4005b8b41c19966dd3bfdb33004bdb2de01c Author: Dave Hansen AuthorDate: Fri, 6 Apr 2018 13:55:13 -0700 Committer: Ingo Molnar CommitDate: Thu, 12 Apr 2018 09:05:58 +0200 x86/mm: Comment _PAGE_GLOBAL mystery I was mystified as to where the _PAGE_GLOBAL in the kernel page tables for kernel text came from. I audited all the places I could find, but I missed one: head_64.S. The page tables that we create in here live for a long time, and they also have _PAGE_GLOBAL set, despite whether the processor supports it or not. It's harmless, and we got *lucky* that the pageattr code accidentally clears it when we wipe it out of __supported_pte_mask and then later try to mark kernel text read-only. Comment some of these properties to make it easier to find and understand in the future. Signed-off-by: Dave Hansen Cc: Andrea Arcangeli Cc: Andy Lutomirski Cc: Arjan van de Ven Cc: Borislav Petkov Cc: Dan Williams Cc: David Woodhouse Cc: Greg Kroah-Hartman Cc: Hugh Dickins Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Kees Cook Cc: Linus Torvalds Cc: Nadav Amit Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20180406205513.079BB265@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/head_64.S | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 48385c1074a5..8344dd2f310a 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -399,8 +399,13 @@ NEXT_PAGE(level3_ident_pgt) .quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC .fill 511, 8, 0 NEXT_PAGE(level2_ident_pgt) - /* Since I easily can, map the first 1G. + /* + * Since I easily can, map the first 1G. * Don't set NX because code runs from these pages. + * + * Note: This sets _PAGE_GLOBAL despite whether + * the CPU supports it or it is enabled. But, + * the CPU should ignore the bit. */ PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD) #else @@ -431,6 +436,10 @@ NEXT_PAGE(level2_kernel_pgt) * (NOTE: at +512MB starts the module area, see MODULES_VADDR. * If you want to increase this then increase MODULES_VADDR * too.) + * + * This table is eventually used by the kernel during normal + * runtime. Care must be taken to clear out undesired bits + * later, like _PAGE_RW or _PAGE_GLOBAL in some cases. */ PMDS(0, __PAGE_KERNEL_LARGE_EXEC, KERNEL_IMAGE_SIZE/PMD_SIZE)