1 files changed, 111 insertions, 0 deletions
diff --git a/arch/x86/include/asm/sync_core.h b/arch/x86/include/asm/sync_core.h
new file mode 100644
index 000000000..ab7382f92
--- /dev/null
+++ b/arch/x86/include/asm/sync_core.h
@@ -0,0 +1,111 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_SYNC_CORE_H
+#define _ASM_X86_SYNC_CORE_H
+
+#include <linux/preempt.h>
+#include <asm/processor.h>
+#include <asm/cpufeature.h>
+#include <asm/special_insns.h>
+
+#ifdef CONFIG_X86_32
+static inline void iret_to_self(void)
+{
+	asm volatile (
+		"pushfl\n\t"
+		"pushl %%cs\n\t"
+		"pushl $1f\n\t"
+		"iret\n\t"
+		"1:"
+		: ASM_CALL_CONSTRAINT : : "memory");
+}
+#else
+static inline void iret_to_self(void)
+{
+	unsigned int tmp;
+
+	asm volatile (
+		"mov %%ss, %0\n\t"
+		"pushq %q0\n\t"
+		"pushq %%rsp\n\t"
+		"addq $8, (%%rsp)\n\t"
+		"pushfq\n\t"
+		"mov %%cs, %0\n\t"
+		"pushq %q0\n\t"
+		"pushq $1f\n\t"
+		"iretq\n\t"
+		"1:"
+		: "=&r" (tmp), ASM_CALL_CONSTRAINT : : "cc", "memory");
+}
+#endif /* CONFIG_X86_32 */
+
+/*
+ * This function forces the icache and prefetched instruction stream to
+ * catch up with reality in two very specific cases:
+ *
+ *  a) Text was modified using one virtual address and is about to be executed
+ *     from the same physical page at a different virtual address.
+ *
+ *  b) Text was modified on a different CPU, may subsequently be
+ *     executed on this CPU, and you want to make sure the new version
+ *     gets executed.  This generally means you're calling this in an IPI.
+ *
+ * If you're calling this for a different reason, you're probably doing
+ * it wrong.
+ *
+ * Like all of Linux's memory ordering operations, this is a
+ * compiler barrier as well.
+ */
+static inline void sync_core(void)
+{
+	/*
+	 * The SERIALIZE instruction is the most straightforward way to
+	 * do this, but it is not universally available.
+	 */
+	if (static_cpu_has(X86_FEATURE_SERIALIZE)) {
+		serialize();
+		return;
+	}
+
+	/*
+	 * For all other processors, there are quite a few ways to do this.
+	 * IRET-to-self is nice because it works on every CPU, at any CPL
+	 * (so it's compatible with paravirtualization), and it never exits
+	 * to a hypervisor.  The only downsides are that it's a bit slow
+	 * (it seems to be a bit more than 2x slower than the fastest
+	 * options) and that it unmasks NMIs.  The "push %cs" is needed,
+	 * because in paravirtual environments __KERNEL_CS may not be a
+	 * valid CS value when we do IRET directly.
+	 *
+	 * In case NMI unmasking or performance ever becomes a problem,
+	 * the next best option appears to be MOV-to-CR2 and an
+	 * unconditional jump.  That sequence also works on all CPUs,
+	 * but it will fault at CPL3 (i.e. Xen PV).
+	 *
+	 * CPUID is the conventional way, but it's nasty: it doesn't
+	 * exist on some 486-like CPUs, and it usually exits to a
+	 * hypervisor.
+	 */
+	iret_to_self();
+}
+
+/*
+ * Ensure that a core serializing instruction is issued before returning
+ * to user-mode. x86 implements return to user-space through sysexit,
+ * sysrel, and sysretq, which are not core serializing.
+ */
+static inline void sync_core_before_usermode(void)
+{
+	/* With PTI, we unconditionally serialize before running user code. */
+	if (static_cpu_has(X86_FEATURE_PTI))
+		return;
+
+	/*
+	 * Even if we're in an interrupt, we might reschedule before returning,
+	 * in which case we could switch to a different thread in the same mm
+	 * and return using SYSRET or SYSEXIT.  Instead of trying to keep
+	 * track of our need to sync the core, just sync right away.
+	 */
+	sync_core();
+}
+
+#endif /* _ASM_X86_SYNC_CORE_H */