Fixes needed to build vboxdrv with kernel 5.8. The changes handle the following kernel API changes:

1. In struct mm_struct, member mmap_sem was renamed to mmap_lock.
2. The information in cpu_tlbstate is no longer exported.
3. The routines __get_vm_area() and map_vm_area() no longer exist and their
   replacements are not exported. Two fixes have been attempted:
   a. The missing routines were not available until kernel 2.6.23, thus the code was
      changed to revert back to the "old" method. Unfortunately, this did not work, and
      likely it will require Oracle to make the changes.
   b. The replacements for __get_vm_area() and map_vm_area() are implemented. The resulting
      code builds but gets missing globals on loading. For testing, the kernel is modified.
      This change cannot be permanent, but it can be temporary.

Index: VirtualBox-6.1.10/src/VBox/Runtime/r0drv/linux/memobj-r0drv-linux.c
===================================================================
--- VirtualBox-6.1.10.orig/src/VBox/Runtime/r0drv/linux/memobj-r0drv-linux.c
+++ VirtualBox-6.1.10/src/VBox/Runtime/r0drv/linux/memobj-r0drv-linux.c
@@ -222,9 +222,17 @@ static void *rtR0MemObjLinuxDoMmap(RTR3P
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 5, 0)
         ulAddr = vm_mmap(NULL, R3PtrFixed, cb, fLnxProt, MAP_SHARED | MAP_ANONYMOUS | MAP_FIXED, 0);
 #else
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
         down_write(&pTask->mm->mmap_sem);
+#else
+        down_write(&pTask->mm->mmap_lock);
+#endif
         ulAddr = do_mmap(NULL, R3PtrFixed, cb, fLnxProt, MAP_SHARED | MAP_ANONYMOUS | MAP_FIXED, 0);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
         up_write(&pTask->mm->mmap_sem);
+#else
+        up_write(&pTask->mm->mmap_lock);
+#endif
 #endif
     }
     else
@@ -232,9 +240,17 @@ static void *rtR0MemObjLinuxDoMmap(RTR3P
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 5, 0)
         ulAddr = vm_mmap(NULL, 0, cb, fLnxProt, MAP_SHARED | MAP_ANONYMOUS, 0);
 #else
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
         down_write(&pTask->mm->mmap_sem);
+#else
+        down_write(&pTask->mm->mmap_lock);
+#endif
         ulAddr = do_mmap(NULL, 0, cb, fLnxProt, MAP_SHARED | MAP_ANONYMOUS, 0);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
         up_write(&pTask->mm->mmap_sem);
+#else
+        up_write(&pTask->mm->mmap_lock);
+#endif
 #endif
         if (    !(ulAddr & ~PAGE_MASK)
             &&  (ulAddr & (uAlignment - 1)))
@@ -269,13 +285,29 @@ static void rtR0MemObjLinuxDoMunmap(void
     Assert(pTask == current); RT_NOREF_PV(pTask);
     vm_munmap((unsigned long)pv, cb);
 #elif defined(USE_RHEL4_MUNMAP)
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
     down_write(&pTask->mm->mmap_sem);
+#else
+    down_write(&pTask->mm->mmap_lock);
+#endif
     do_munmap(pTask->mm, (unsigned long)pv, cb, 0); /* should it be 1 or 0? */
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
     up_write(&pTask->mm->mmap_sem);
 #else
+    up_write(&pTask->mm->mmap_lock);
+#endif
+#else
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
     down_write(&pTask->mm->mmap_sem);
+#else
+    down_write(&pTask->mm->mmap_lock);
+#endif
     do_munmap(pTask->mm, (unsigned long)pv, cb);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
     up_write(&pTask->mm->mmap_sem);
+#else
+    up_write(&pTask->mm->mmap_lock);
+#endif
 #endif
 }
 
@@ -593,7 +625,11 @@ DECLHIDDEN(int) rtR0MemObjNativeFree(RTR
                 size_t              iPage;
                 Assert(pTask);
                 if (pTask && pTask->mm)
-                    down_read(&pTask->mm->mmap_sem);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+		    down_read(&pTask->mm->mmap_sem);
+#else
+		    down_read(&pTask->mm->mmap_lock);
+#endif
 
                 iPage = pMemLnx->cPages;
                 while (iPage-- > 0)
@@ -608,7 +644,11 @@ DECLHIDDEN(int) rtR0MemObjNativeFree(RTR
                 }
 
                 if (pTask && pTask->mm)
-                    up_read(&pTask->mm->mmap_sem);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+		    up_read(&pTask->mm->mmap_sem);
+#else
+		    up_read(&pTask->mm->mmap_lock);
+#endif
             }
             /* else: kernel memory - nothing to do here. */
             break;
@@ -1076,7 +1116,11 @@ DECLHIDDEN(int) rtR0MemObjNativeLockUser
     papVMAs = (struct vm_area_struct **)RTMemAlloc(sizeof(*papVMAs) * cPages);
     if (papVMAs)
     {
-        down_read(&pTask->mm->mmap_sem);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+	down_read(&pTask->mm->mmap_sem);
+#else
+	down_read(&pTask->mm->mmap_lock);
+#endif
 
         /*
          * Get user pages.
@@ -1162,7 +1206,11 @@ DECLHIDDEN(int) rtR0MemObjNativeLockUser
                 papVMAs[rc]->vm_flags |= VM_DONTCOPY | VM_LOCKED;
             }
 
-            up_read(&pTask->mm->mmap_sem);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+	    up_read(&pTask->mm->mmap_sem);
+#else
+	    up_read(&pTask->mm->mmap_lock);
+#endif
 
             RTMemFree(papVMAs);
 
@@ -1189,7 +1237,11 @@ DECLHIDDEN(int) rtR0MemObjNativeLockUser
 #endif
         }
 
-        up_read(&pTask->mm->mmap_sem);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+	up_read(&pTask->mm->mmap_sem);
+#else
+	up_read(&pTask->mm->mmap_lock);
+#endif
 
         RTMemFree(papVMAs);
         rc = VERR_LOCK_FAILED;
@@ -1604,7 +1656,11 @@ DECLHIDDEN(int) rtR0MemObjNativeMapUser(
             const size_t    cPages    = (offSub + cbSub) >> PAGE_SHIFT;
             size_t          iPage;
 
-            down_write(&pTask->mm->mmap_sem);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+	    down_write(&pTask->mm->mmap_sem);
+#else
+	    down_write(&pTask->mm->mmap_lock);
+#endif
 
             rc = VINF_SUCCESS;
             if (pMemLnxToMap->cPages)
@@ -1721,7 +1777,11 @@ DECLHIDDEN(int) rtR0MemObjNativeMapUser(
             }
 #endif /* CONFIG_NUMA_BALANCING */
 
-            up_write(&pTask->mm->mmap_sem);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+	    up_write(&pTask->mm->mmap_sem);
+#else
+	    up_write(&pTask->mm->mmap_lock);
+#endif
 
             if (RT_SUCCESS(rc))
             {
Index: VirtualBox-6.1.10/src/VBox/HostDrivers/Support/linux/SUPDrv-linux.c
===================================================================
--- VirtualBox-6.1.10.orig/src/VBox/HostDrivers/Support/linux/SUPDrv-linux.c
+++ VirtualBox-6.1.10/src/VBox/HostDrivers/Support/linux/SUPDrv-linux.c
@@ -757,12 +757,19 @@ EXPORT_SYMBOL(SUPDrvLinuxIDC);
 RTCCUINTREG VBOXCALL supdrvOSChangeCR4(RTCCUINTREG fOrMask, RTCCUINTREG fAndMask)
 {
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 20, 0)
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
     RTCCUINTREG uOld = this_cpu_read(cpu_tlbstate.cr4);
+#else
+    RTCCUINTREG uOld = __read_cr4();
+#endif
     RTCCUINTREG uNew = (uOld & fAndMask) | fOrMask;
     if (uNew != uOld)
     {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
         this_cpu_write(cpu_tlbstate.cr4, uNew);
         __write_cr4(uNew);
+#endif
+        ASMSetCR4(uNew);
     }
 #else
     RTCCUINTREG uOld = ASMGetCR4();
Index: VirtualBox-6.1.10/src/VBox/Runtime/r0drv/linux/alloc-r0drv-linux.c
===================================================================
--- VirtualBox-6.1.10.orig/src/VBox/Runtime/r0drv/linux/alloc-r0drv-linux.c
+++ VirtualBox-6.1.10/src/VBox/Runtime/r0drv/linux/alloc-r0drv-linux.c
@@ -168,7 +168,12 @@ static PRTMEMHDR rtR0MemAllocExecVmArea(
     struct vm_struct   *pVmArea;
     size_t              iPage;
 
+# if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
+    pVmArea = __get_vm_area_caller(cbAlloc, VM_ALLOC, MODULES_VADDR, MODULES_END,
+				  __builtin_return_address(0));
+#else
     pVmArea = __get_vm_area(cbAlloc, VM_ALLOC, MODULES_VADDR, MODULES_END);
+#endif
     if (!pVmArea)
         return NULL;
     pVmArea->nr_pages = 0;    /* paranoia? */
@@ -201,6 +206,12 @@ static PRTMEMHDR rtR0MemAllocExecVmArea(
 # endif
         pVmArea->nr_pages = cPages;
         pVmArea->pages    = papPages;
+# if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
+	unsigned long start = (unsigned long)pVmArea->addr;
+	unsigned long size = get_vm_area_size(pVmArea);
+
+	if (!map_kernel_range(start, size, PAGE_KERNEL_EXEC, papPages))
+#else
         if (!map_vm_area(pVmArea, PAGE_KERNEL_EXEC,
 # if LINUX_VERSION_CODE < KERNEL_VERSION(3, 17, 0)
                          &papPagesIterator
@@ -208,6 +219,7 @@ static PRTMEMHDR rtR0MemAllocExecVmArea(
                          papPages
 # endif
                          ))
+#endif
         {
             PRTMEMLNXHDREX pHdrEx = (PRTMEMLNXHDREX)pVmArea->addr;
             pHdrEx->pVmArea     = pVmArea;