x86/mm: Disallow running with 32-bit PTEs to work around erratum

[cascardo/linux.git] / arch / x86 / boot / cpucheck.c

diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
index 1fd7d57..4ad7d70 100644 (file)
--- 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;
+}
+
+