linux-kernel - [PATCH 2/2] x86: Quark: Comment setup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1412120517-14738-3-git-send-email-pure.logic@nexus-software.ie>
Date:	Wed,  1 Oct 2014 00:41:57 +0100
From:	Bryan O'Donoghue <pure.logic@...us-software.ie>
To:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	davej@...hat.com, hmh@....eng.br
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Bryan O'Donoghue <pure.logic@...us-software.ie>
Subject: [PATCH 2/2] x86: Quark: Comment setup_arch for TLB/PGE bugfix

Quark X1000 requires CR3 to be rewritten to flush TLB entries
irrespective of the PGE bits in CR4 or PTE.PGE

Add a comment to setup_arch to indicate that the code

load_cr3(swapper_pg_dir);
__flush_tlb_all();

Will already have flushed the TLB @ the CR3 reload allowing us
to skip over a potential if/else for Quark.

This comment clearly states the bug, the behaviour we rely on
and the reason why we only do it this way - one time.

Later on cpu_has_pge() will be false due to a fixup in
intel_init_early() and __flush_tlb_all() will work as expected
from that point onwards

Signed-off-by: Bryan O'Donoghue <pure.logic@...us-software.ie>
---
 arch/x86/kernel/setup.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 41ead8d..235cfd3 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -879,6 +879,15 @@ void __init setup_arch(char **cmdline_p)
 			KERNEL_PGD_PTRS);
 
 	load_cr3(swapper_pg_dir);
+	/*
+	 * Note: Quark X1000 CPUs advertise PGE incorrectly and require
+	 * a cr3 based tlb flush, so the following __flush_tlb_all()
+	 * will not flush anything because the cpu quirk which clears
+	 * X86_FEATURE_PGE has not been invoked yet. Though due to the
+	 * load_cr3() above the TLB has been flushed already. The
+	 * quirk is invoked before subsequent calls to __flush_tlb_all()
+	 * so proper operation is guaranteed.
+	 */
 	__flush_tlb_all();
 #else
 	printk(KERN_INFO "Command line: %s\n", boot_command_line);
-- 
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/