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x86/boot/compressed/64: Describe the logic behind the LA57 check 

The patch explains the LA57 check in more details.

Tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180226180451.86788-2-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kirill A. Shutemov 2018-02-26 21:04:47 +03:00 committed by Ingo Molnar
parent ae8d1d0061
commit a403d79818
1 changed files with 15 additions and 3 deletions
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18
arch/x86/boot/compressed/pgtable_64.c
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@ -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;
}