Commit-ID: a403d798182f4f7be5e9bab56cfa37e9828fd92a Gitweb: https://git.kernel.org/tip/a403d798182f4f7be5e9bab56cfa37e9828fd92a Author: Kirill A. Shutemov <kirill.shute...@linux.intel.com> AuthorDate: Mon, 26 Feb 2018 21:04:47 +0300 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Mon, 12 Mar 2018 09:29:24 +0100
x86/boot/compressed/64: Describe the logic behind the LA57 check The patch explains the LA57 check in more details. Tested-by: Borislav Petkov <b...@suse.de> Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Andy Shevchenko <andy.shevche...@gmail.com> Cc: Cyrill Gorcunov <gorcu...@openvz.org> Cc: Eric Biederman <ebied...@xmission.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Juergen Gross <jgr...@suse.com> Cc: Kees Cook <keesc...@chromium.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Matthew Wilcox <wi...@infradead.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: linux...@kvack.org Link: http://lkml.kernel.org/r/20180226180451.86788-2-kirill.shute...@linux.intel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- 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; }
