Kernel: Move Kernel/Arch/x86/SafeMem.h to Kernel/Arch/SafeMem.h

The file does not contain any specific architectural code, thus it can
be moved to the Kernel/Arch directory.

Kernel/Arch/SafeMem.h

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Atomic.h>
+#include <AK/Optional.h>
+#include <AK/Types.h>
+
+#pragma once
+
+namespace Kernel {
+
+struct RegisterState;
+
+[[nodiscard]] bool safe_memcpy(void* dest_ptr, void const* src_ptr, size_t n, void*& fault_at) __attribute__((used));
+[[nodiscard]] ssize_t safe_strnlen(char const* str, size_t max_n, void*& fault_at) __attribute__((used));
+[[nodiscard]] bool safe_memset(void* dest_ptr, int c, size_t n, void*& fault_at) __attribute__((used));
+[[nodiscard]] Optional<u32> safe_atomic_fetch_add_relaxed(u32 volatile* var, u32 val) __attribute__((used));
+[[nodiscard]] Optional<u32> safe_atomic_exchange_relaxed(u32 volatile* var, u32 val) __attribute__((used));
+[[nodiscard]] Optional<u32> safe_atomic_load_relaxed(u32 volatile* var) __attribute__((used));
+[[nodiscard]] bool safe_atomic_store_relaxed(u32 volatile* var, u32 val) __attribute__((used));
+[[nodiscard]] Optional<bool> safe_atomic_compare_exchange_relaxed(u32 volatile* var, u32& expected, u32 val) __attribute__((used));
+
+[[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_and_relaxed(u32 volatile* var, u32 val)
+{
+    auto expected_value = safe_atomic_load_relaxed(var);
+    if (!expected_value.has_value())
+        return {}; // fault
+    u32& expected = expected_value.value();
+    for (;;) {
+        auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected & val);
+        if (!result.has_value())
+            return {}; // fault
+        if (result.value())
+            return expected; // exchanged
+
+        // This is only so that we don't saturate the bus...
+        AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
+    }
+}
+
+[[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_and_not_relaxed(u32 volatile* var, u32 val)
+{
+    auto expected_value = safe_atomic_load_relaxed(var);
+    if (!expected_value.has_value())
+        return {}; // fault
+    u32& expected = expected_value.value();
+    for (;;) {
+        auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected & ~val);
+        if (!result.has_value())
+            return {}; // fault
+        if (result.value())
+            return expected; // exchanged
+
+        // This is only so that we don't saturate the bus...
+        AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
+    }
+}
+
+[[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_or_relaxed(u32 volatile* var, u32 val)
+{
+    auto expected_value = safe_atomic_load_relaxed(var);
+    if (!expected_value.has_value())
+        return {}; // fault
+    u32& expected = expected_value.value();
+    for (;;) {
+        auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected | val);
+        if (!result.has_value())
+            return {}; // fault
+        if (result.value())
+            return expected; // exchanged
+
+        // This is only so that we don't saturate the bus...
+        AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
+    }
+}
+
+[[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_xor_relaxed(u32 volatile* var, u32 val)
+{
+    auto expected_value = safe_atomic_load_relaxed(var);
+    if (!expected_value.has_value())
+        return {}; // fault
+    u32& expected = expected_value.value();
+    for (;;) {
+        auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected ^ val);
+        if (!result.has_value())
+            return {}; // fault
+        if (result.value())
+            return expected; // exchanged
+
+        // This is only so that we don't saturate the bus...
+        AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
+    }
+}
+
+bool handle_safe_access_fault(RegisterState& regs, FlatPtr fault_address);
+
+}