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Message-ID: <tip-e4a84be6f05eab4778732d799f63b3cd15427885@git.kernel.org>
Date: Wed, 13 Jul 2016 01:04:13 -0700
From: tip-bot for Dave Hansen <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: jpoimboe@...hat.com, bp@...en8.de, torvalds@...ux-foundation.org,
brgerst@...il.com, luto@...nel.org, hpa@...or.com,
dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, peterz@...radead.org, mcgrof@...e.com,
tglx@...utronix.de, dave@...1.net, toshi.kani@...com,
dvlasenk@...hat.com, mingo@...nel.org
Subject: [tip:x86/mm] x86/mm: Disallow running with 32-bit PTEs to work
around erratum
Commit-ID: e4a84be6f05eab4778732d799f63b3cd15427885
Gitweb: http://git.kernel.org/tip/e4a84be6f05eab4778732d799f63b3cd15427885
Author: Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate: Thu, 7 Jul 2016 17:19:14 -0700
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 13 Jul 2016 09:43:25 +0200
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@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave@...1.net>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@...e.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Toshi Kani <toshi.kani@...com>
Cc: dave.hansen@...el.com
Cc: linux-mm@...ck.org
Cc: mhocko@...e.com
Link: http://lkml.kernel.org/r/20160708001914.D0B50110@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
arch/x86/boot/boot.h | 1 +
arch/x86/boot/cpu.c | 2 ++
arch/x86/boot/cpucheck.c | 33 +++++++++++++++++++++++++++++++++
arch/x86/boot/cpuflags.c | 1 +
arch/x86/boot/cpuflags.h | 1 +
5 files changed, 38 insertions(+)
diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 9011a88..a5ce666 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -294,6 +294,7 @@ static inline int cmdline_find_option_bool(const char *option)
/* cpu.c, cpucheck.c */
int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr);
+int check_knl_erratum(void);
int validate_cpu(void);
/* early_serial_console.c */
diff --git a/arch/x86/boot/cpu.c b/arch/x86/boot/cpu.c
index 29207f6..26240dd 100644
--- a/arch/x86/boot/cpu.c
+++ b/arch/x86/boot/cpu.c
@@ -93,6 +93,8 @@ int validate_cpu(void)
show_cap_strs(err_flags);
putchar('\n');
return -1;
+ } else if (check_knl_erratum()) {
+ return -1;
} else {
return 0;
}
diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
index 1fd7d57..4ad7d70 100644
--- a/arch/x86/boot/cpucheck.c
+++ b/arch/x86/boot/cpucheck.c
@@ -24,6 +24,7 @@
# include "boot.h"
#endif
#include <linux/types.h>
+#include <asm/intel-family.h>
#include <asm/processor-flags.h>
#include <asm/required-features.h>
#include <asm/msr-index.h>
@@ -175,6 +176,8 @@ int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr)
puts("WARNING: PAE disabled. Use parameter 'forcepae' to enable at your own risk!\n");
}
}
+ if (!err)
+ err = check_knl_erratum();
if (err_flags_ptr)
*err_flags_ptr = err ? err_flags : NULL;
@@ -185,3 +188,33 @@ int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr)
return (cpu.level < req_level || err) ? -1 : 0;
}
+
+int check_knl_erratum(void)
+{
+ /*
+ * First check for the affected model/family:
+ */
+ if (!is_intel() ||
+ cpu.family != 6 ||
+ cpu.model != INTEL_FAM6_XEON_PHI_KNL)
+ return 0;
+
+ /*
+ * This erratum affects the Accessed/Dirty bits, and can
+ * cause stray bits to be set in !Present PTEs. We have
+ * enough bits in our 64-bit PTEs (which we have on real
+ * 64-bit mode or PAE) to avoid using these troublesome
+ * bits. But, we do not have enough space in our 32-bit
+ * PTEs. So, refuse to run on 32-bit non-PAE kernels.
+ */
+ if (IS_ENABLED(CONFIG_X86_64) || IS_ENABLED(CONFIG_X86_PAE))
+ return 0;
+
+ puts("This 32-bit kernel can not run on this Xeon Phi x200\n"
+ "processor due to a processor erratum. Use a 64-bit\n"
+ "kernel, or enable PAE in this 32-bit kernel.\n\n");
+
+ return -1;
+}
+
+
diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index 431fa5f..6687ab9 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -102,6 +102,7 @@ void get_cpuflags(void)
cpuid(0x1, &tfms, &ignored, &cpu.flags[4],
&cpu.flags[0]);
cpu.level = (tfms >> 8) & 15;
+ cpu.family = cpu.level;
cpu.model = (tfms >> 4) & 15;
if (cpu.level >= 6)
cpu.model += ((tfms >> 16) & 0xf) << 4;
diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
index 4cb404f..15ad56a 100644
--- a/arch/x86/boot/cpuflags.h
+++ b/arch/x86/boot/cpuflags.h
@@ -6,6 +6,7 @@
struct cpu_features {
int level; /* Family, or 64 for x86-64 */
+ int family; /* Family, always */
int model;
u32 flags[NCAPINTS];
};
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