From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754048AbeB0Pma (ORCPT ); Tue, 27 Feb 2018 10:42:30 -0500 Received: from mga06.intel.com ([134.134.136.31]:57348 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753924AbeB0Pm2 (ORCPT ); Tue, 27 Feb 2018 10:42:28 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.47,401,1515484800"; d="scan'208";a="33220319" From: "Kirill A. Shutemov" To: Ingo Molnar , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" Cc: Linus Torvalds , Andy Lutomirski , Cyrill Gorcunov , Borislav Petkov , Andi Kleen , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" Subject: [PATCHv2 1/5] x86/boot/compressed/64: Describe the logic behind LA57 check Date: Tue, 27 Feb 2018 18:42:13 +0300 Message-Id: <20180227154217.69347-2-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180227154217.69347-1-kirill.shutemov@linux.intel.com> References: <20180227154217.69347-1-kirill.shutemov@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The patch explains the LA57 check in more details. Signed-off-by: Kirill A. Shutemov --- arch/x86/boot/compressed/pgtable_64.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c index 3f1697fcc7a8..45c76eff2718 100644 --- a/arch/x86/boot/compressed/pgtable_64.c +++ b/arch/x86/boot/compressed/pgtable_64.c @@ -18,10 +18,22 @@ struct paging_config paging_prepare(void) { struct paging_config paging_config = {}; - /* Check if LA57 is desired and supported */ - if (IS_ENABLED(CONFIG_X86_5LEVEL) && native_cpuid_eax(0) >= 7 && - (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) + /* + * Check if LA57 is desired and supported. + * + * There are two parts to the check: + * - if the kernel supports 5-level paging: CONFIG_X86_5LEVEL=y + * - if the machine supports 5-level paging: + * + CPUID leaf 7 is supported + * + the leaf has the feature bit set + * + * That's substitute for boot_cpu_has() in early boot code. + */ + if (IS_ENABLED(CONFIG_X86_5LEVEL) && + native_cpuid_eax(0) >= 7 && + (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) { paging_config.l5_required = 1; + } return paging_config; } -- 2.16.1