[PATCH v2 1/2] x86/boot: Fix another __read_cr4() case on 486

From	Andy Lutomirski <luto@kernel.org>
Newsgroups	linux.kernel
Subject	[PATCH v2 1/2] x86/boot: Fix another __read_cr4() case on 486
Date	2016-09-29 21:50 +0200
Message-ID	<smPvb-8lN-3@gated-at.bofh.it> (permalink)
References	<smPvb-8lN-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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The condition for reading CR4 was wrong: there are some CPUs with
CPUID but not CR4.  Rather than trying to make the condition exact,
using __read_cr4_safe().

Reported-by: david@saggiorato.net
Fixes: 18bc7bd523e0 ("x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features directly")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/kernel/setup.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 0fa60f5f5a16..98c9cd6f3b5d 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1137,9 +1137,7 @@ void __init setup_arch(char **cmdline_p)
 	 * auditing all the early-boot CR4 manipulation would be needed to
 	 * rule it out.
 	 */
-	if (boot_cpu_data.cpuid_level >= 0)
-		/* A CPU has %cr4 if and only if it has CPUID. */
-		mmu_cr4_features = __read_cr4();
+	mmu_cr4_features = __read_cr4_safe();
 
 	memblock_set_current_limit(get_max_mapped());
 
-- 
2.7.4

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[PATCH v2 1/2] x86/boot: Fix another __read_cr4() case on 486 Andy Lutomirski <luto@kernel.org> - 2016-09-29 21:50 +0200
  Re: [PATCH v2 1/2] x86/boot: Fix another __read_cr4() case on 486 Borislav Petkov <bp@alien8.de> - 2016-09-30 00:40 +0200
  [tip:x86/urgent] x86/boot: Fix another __read_cr4() case on 486 tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-30 12:50 +0200

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