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authorDave Hansen <dave.hansen@linux.intel.com>2016-07-07 17:19:14 -0700
committerIngo Molnar <mingo@kernel.org>2016-07-13 09:43:25 +0200
commite4a84be6f05eab4778732d799f63b3cd15427885 (patch)
tree7b5c31fb9264f7daf0b66284a2392bb46e11e321 /arch/x86/boot/cpuflags.c
parent97e3c602ccbdd7db54e92fe05675c664c052a466 (diff)
downloadlinux-e4a84be6f05eab4778732d799f63b3cd15427885.tar.bz2
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>
Diffstat (limited to 'arch/x86/boot/cpuflags.c')
-rw-r--r--arch/x86/boot/cpuflags.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index 431fa5f84537..6687ab953257 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;