linux-stable/arch/x86/boot/cpu.c
Dave Hansen e4a84be6f0 x86/mm: Disallow running with 32-bit PTEs to work around erratum
The Intel(R) Xeon Phi(TM) Processor x200 Family (codename: Knights
Landing) has an erratum where a processor thread setting the Accessed
or Dirty bits may not do so atomically against its checks for the
Present bit.  This may cause a thread (which is about to page fault)
to set A and/or D, even though the Present bit had already been
atomically cleared.

These bits are truly "stray".  In the case of the Dirty bit, the
thread associated with the stray set was *not* allowed to write to
the page.  This means that we do not have to launder the bit(s); we
can simply ignore them.

If the PTE is used for storing a swap index or a NUMA migration index,
the A bit could be misinterpreted as part of the swap type.  The stray
bits being set cause a software-cleared PTE to be interpreted as a
swap entry.  In some cases (like when the swap index ends up being
for a non-existent swapfile), the kernel detects the stray value
and WARN()s about it, but there is no guarantee that the kernel can
always detect it.

When we have 64-bit PTEs (64-bit mode or 32-bit PAE), we were able
to move the swap PTE format around to avoid these troublesome bits.
But, 32-bit non-PAE is tight on bits.  So, disallow it from running
on this hardware.  I can't imagine anyone wanting to run 32-bit
non-highmem kernels on this hardware, but disallowing them from
running entirely is surely the safe thing to do.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: dave.hansen@intel.com
Cc: linux-mm@kvack.org
Cc: mhocko@suse.com
Link: http://lkml.kernel.org/r/20160708001914.D0B50110@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-07-13 09:43:25 +02:00

101 lines
2.1 KiB
C

/* -*- linux-c -*- ------------------------------------------------------- *
*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright 2007-2008 rPath, Inc. - All Rights Reserved
*
* This file is part of the Linux kernel, and is made available under
* the terms of the GNU General Public License version 2.
*
* ----------------------------------------------------------------------- */
/*
* arch/x86/boot/cpu.c
*
* Check for obligatory CPU features and abort if the features are not
* present.
*/
#include "boot.h"
#ifdef CONFIG_X86_FEATURE_NAMES
#include "cpustr.h"
#endif
static char *cpu_name(int level)
{
static char buf[6];
if (level == 64) {
return "x86-64";
} else {
if (level == 15)
level = 6;
sprintf(buf, "i%d86", level);
return buf;
}
}
static void show_cap_strs(u32 *err_flags)
{
int i, j;
#ifdef CONFIG_X86_FEATURE_NAMES
const unsigned char *msg_strs = (const unsigned char *)x86_cap_strs;
for (i = 0; i < NCAPINTS; i++) {
u32 e = err_flags[i];
for (j = 0; j < 32; j++) {
if (msg_strs[0] < i ||
(msg_strs[0] == i && msg_strs[1] < j)) {
/* Skip to the next string */
msg_strs += 2;
while (*msg_strs++)
;
}
if (e & 1) {
if (msg_strs[0] == i &&
msg_strs[1] == j &&
msg_strs[2])
printf("%s ", msg_strs+2);
else
printf("%d:%d ", i, j);
}
e >>= 1;
}
}
#else
for (i = 0; i < NCAPINTS; i++) {
u32 e = err_flags[i];
for (j = 0; j < 32; j++) {
if (e & 1)
printf("%d:%d ", i, j);
e >>= 1;
}
}
#endif
}
int validate_cpu(void)
{
u32 *err_flags;
int cpu_level, req_level;
check_cpu(&cpu_level, &req_level, &err_flags);
if (cpu_level < req_level) {
printf("This kernel requires an %s CPU, ",
cpu_name(req_level));
printf("but only detected an %s CPU.\n",
cpu_name(cpu_level));
return -1;
}
if (err_flags) {
puts("This kernel requires the following features "
"not present on the CPU:\n");
show_cap_strs(err_flags);
putchar('\n');
return -1;
} else if (check_knl_erratum()) {
return -1;
} else {
return 0;
}
}