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--- a/arch/x86/kernel/cpu/bugs.c 2019-07-18 12:58:03.000000000 -0700
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+++ b/arch/x86/kernel/cpu/bugs.c 2019-08-07 23:20:28.694377902 -0700
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@@ -28,7 +28,70 @@
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#include <asm/intel-family.h>
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#include <linux/prctl.h>
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#include <linux/sched/smt.h>
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+
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+static int __init no_387(char *s)
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+{
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+ boot_cpu_data.hard_math = 0;
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+ write_cr0(X86_CR0_TS | X86_CR0_EM | X86_CR0_MP | read_cr0());
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+ return 1;
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+}
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+
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+__setup("no387", no_387);
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+
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+static double __initdata x = 4195835.0;
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+static double __initdata y = 3145727.0;
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+
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+/*
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+ * This used to check for exceptions..
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+ * However, it turns out that to support that,
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+ * the XMM trap handlers basically had to
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+ * be buggy. So let's have a correct XMM trap
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+ * handler, and forget about printing out
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+ * some status at boot.
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+ *
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+ * We should really only care about bugs here
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+ * anyway. Not features.
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+ */
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+static void __init check_fpu(void)
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+{
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+ s32 fdiv_bug;
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+
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+ if (!boot_cpu_data.hard_math) {
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+#ifndef CONFIG_MATH_EMULATION
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+ pr_emerg("No coprocessor found and no math emulation present\n");
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+ pr_emerg("Giving up\n");
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+ for (;;) ;
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+#endif
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+ return;
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+ }
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+ kernel_fpu_begin();
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+
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+ /*
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+ * trap_init() enabled FXSR and company _before_ testing for FP
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+ * problems here.
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+ *
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+ * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug
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+ */
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+ __asm__("fninit\n\t"
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+ "fldl %1\n\t"
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+ "fdivl %2\n\t"
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+ "fmull %2\n\t"
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+ "fldl %1\n\t"
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+ "fsubp %%st,%%st(1)\n\t"
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+ "fistpl %0\n\t"
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+ "fwait\n\t"
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+ "fninit"
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+ : "=m" (*&fdiv_bug)
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+ : "m" (*&x), "m" (*&y);;
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+
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+ kernel_fpu_end();
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+
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+ if (fdiv_bug) {
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+ set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
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+ pr_warn("Hmm, FPU with FDIV bug\n");
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+ }
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+}
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static void __init spectre_v1_select_mitigation(void);
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static void __init spectre_v2_select_mitigation(void);
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@@ -926,8 +989,10 @@ static ssize_t cpu_show_common(struct de
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switch (bug) {
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case X86_BUG_CPU_MELTDOWN:
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+#ifdef CONFIG_KAISER
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if (kaiser_enabled)
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return sprintf(buf, "Mitigation: PTI\n");
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+#endif
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break;
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