From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id BA9B06B000C for ; Mon, 26 Feb 2018 13:05:04 -0500 (EST) Received: by mail-pg0-f70.google.com with SMTP id i11so5831071pgq.10 for ; Mon, 26 Feb 2018 10:05:04 -0800 (PST) Received: from mga18.intel.com (mga18.intel.com. [134.134.136.126]) by mx.google.com with ESMTPS id r2si5761764pgp.704.2018.02.26.10.05.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Feb 2018 10:05:03 -0800 (PST) From: "Kirill A. Shutemov" Subject: [PATCH 1/5] x86/boot/compressed/64: Describe the logic behind LA57 check Date: Mon, 26 Feb 2018 21:04:47 +0300 Message-Id: <20180226180451.86788-2-kirill.shutemov@linux.intel.com> In-Reply-To: <20180226180451.86788-1-kirill.shutemov@linux.intel.com> References: <20180226180451.86788-1-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Borislav Petkov Cc: Linus Torvalds , Andy Lutomirski , Cyrill Gorcunov , Andi Kleen , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org