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From: Andy Lutomirski <luto@kernel.org>
To: x86@kernel.org
Cc: david@saggiorato.net, Borislav Petkov <bp@alien8.de>,
	Brian Gerst <brgerst@gmail.com>,
	linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>
Subject: [PATCH v2 1/2] x86/boot: Fix another __read_cr4() case on 486
Date: Thu, 29 Sep 2016 12:48:11 -0700
Message-ID: <8c453a61c4f44ab6ff43c29780ba04835234d2e5.1475178369.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1475178369.git.luto@kernel.org>
In-Reply-To: <cover.1475178369.git.luto@kernel.org>

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

  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-29 19:48 [PATCH v2 0/2] CR4 fixes (one is urgent) Andy Lutomirski
2016-09-29 19:48 ` Andy Lutomirski [this message]
2016-09-29 22:38   ` [PATCH v2 1/2] x86/boot: Fix another __read_cr4() case on 486 Borislav Petkov
2016-09-30 10:43   ` [tip:x86/urgent] " tip-bot for Andy Lutomirski
2016-09-29 19:48 ` [PATCH v2 2/2] x86/asm: Get rid of __read_cr4_safe() Andy Lutomirski
2016-09-30 10:45   ` [tip:x86/asm] " tip-bot for Andy Lutomirski

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