Add initial support for kernel 6.15.0.
Patch obtained by comparing sources from 7.1.8 and 7.2.0_BETA1 where upstream added support.
https://bugs.gentoo.org/956675

--- a/vboxdrv/Makefile-footer.gmk
+++ b/vboxdrv/Makefile-footer.gmk
@@ -115,6 +115,7 @@ VBOXMOD_EXT := ko
 
 # build defs
 EXTRA_CFLAGS += $(VBOXMOD_CFLAGS) $(addprefix -I,$(KERN_INCL) $(VBOXMOD_INCL)) $(VBOXMOD_0_KFLAGS) $(KDEBUG)
+ccflags-y += $(EXTRA_CFLAGS)
 $(VBOXMOD_0_TARGET)-y := $(VBOXMOD_OBJS)
 obj-m += $(VBOXMOD_0_TARGET).o
 
--- a/vboxdrv/r0drv/linux/timer-r0drv-linux.c
+++ b/vboxdrv/r0drv/linux/timer-r0drv-linux.c
@@ -422,7 +422,11 @@ static void rtTimerLnxStopSubTimer(PRTTIMERLNXSUBTIMER pSubTimer, bool fHighRes)
     }
     else
 #endif
+# if RTLNX_VER_MIN(6,15,0)
+        timer_delete(&pSubTimer->u.Std.LnxTimer);
+#else
         del_timer(&pSubTimer->u.Std.LnxTimer);
+#endif
 
     rtTimerLnxSetState(&pSubTimer->enmState, RTTIMERLNXSTATE_STOPPED);
 }
@@ -470,7 +474,11 @@ static void rtTimerLnxDestroyIt(PRTTIMER pTimer)
             hrtimer_cancel(&pTimer->aSubTimers[iCpu].u.Hr.LnxTimer);
         else
 #endif
+# if RTLNX_VER_MIN(6,15,0)
+            timer_delete_sync(&pTimer->aSubTimers[iCpu].u.Std.LnxTimer);
+#else
             del_timer_sync(&pTimer->aSubTimers[iCpu].u.Std.LnxTimer);
+#endif
     }
 
     /*
@@ -1626,8 +1634,13 @@ RTDECL(int) RTTimerCreateEx(PRTTIMER *ppTimer, uint64_t u64NanoInterval, uint32_
 #ifdef RTTIMER_LINUX_WITH_HRTIMER
         if (pTimer->fHighRes)
         {
+#if RTLNX_VER_MIN(6,15,0)
+            hrtimer_setup(&pTimer->aSubTimers[iCpu].u.Hr.LnxTimer,
+                          rtTimerLinuxHrCallback, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+#else
             hrtimer_init(&pTimer->aSubTimers[iCpu].u.Hr.LnxTimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
             pTimer->aSubTimers[iCpu].u.Hr.LnxTimer.function     = rtTimerLinuxHrCallback;
+#endif
         }
         else
 #endif
--- a/vboxnetadp/Makefile-footer.gmk
+++ b/vboxnetadp/Makefile-footer.gmk
@@ -115,6 +115,7 @@ VBOXMOD_EXT := ko
 
 # build defs
 EXTRA_CFLAGS += $(VBOXMOD_CFLAGS) $(addprefix -I,$(KERN_INCL) $(VBOXMOD_INCL)) $(VBOXMOD_0_KFLAGS) $(KDEBUG)
+ccflags-y += $(EXTRA_CFLAGS)
 $(VBOXMOD_0_TARGET)-y := $(VBOXMOD_OBJS)
 obj-m += $(VBOXMOD_0_TARGET).o
 
--- a/vboxnetflt/Makefile-footer.gmk
+++ b/vboxnetflt/Makefile-footer.gmk
@@ -115,6 +115,7 @@ VBOXMOD_EXT := ko
 
 # build defs
 EXTRA_CFLAGS += $(VBOXMOD_CFLAGS) $(addprefix -I,$(KERN_INCL) $(VBOXMOD_INCL)) $(VBOXMOD_0_KFLAGS) $(KDEBUG)
+ccflags-y += $(EXTRA_CFLAGS)
 $(VBOXMOD_0_TARGET)-y := $(VBOXMOD_OBJS)
 obj-m += $(VBOXMOD_0_TARGET).o
 
--- a/vboxdrv/linux/SUPDrv-linux.c
+++ b/vboxdrv/linux/SUPDrv-linux.c
@@ -1744,10 +1744,17 @@ SUPR0DECL(bool) SUPR0FpuBegin(bool fCtxHook)
      */
     Assert(fCtxHook || !RTThreadPreemptIsEnabled(NIL_RTTHREAD));
     kernel_fpu_begin();
-# if 0 /* Always do it for now for better test coverage. */
+#  if RTLNX_VER_MIN(6,15,0) /* fpregs_unlock may do more than just preempt_enable, so only when necessary now. */
     if (fCtxHook)
-# endif
+#  endif
+    {
+#  if RTLNX_VER_MIN(6,15,0)
+        if (!irqs_disabled())
+            fpregs_unlock();
+#  else
         preempt_enable();
+#  endif
+    }
     return false; /** @todo Not sure if we have license to use any extended state, or
                    *        if we're limited to the SSE & x87 FPU. If it's the former,
                    *        we should return @a true and the caller can skip
@@ -1765,10 +1772,17 @@ SUPR0DECL(void) SUPR0FpuEnd(bool fCtxHook)
 #if RTLNX_VER_MIN(4,19,0)
     /* HACK ALERT! See SUPR0FpuBegin for an explanation of this. */
     Assert(!RTThreadPreemptIsEnabled(NIL_RTTHREAD));
-# if 0 /* Always do it for now for better test coverage. */
+#  if RTLNX_VER_MIN(6,15,0) /* fpregs_unlock may do more than just preempt_enable, so only when necessary now. */
     if (fCtxHook)
-# endif
+#  endif
+    {
+#  if RTLNX_VER_MIN(6,15,0)
+        if (!irqs_disabled())
+            fpregs_lock();
+#  else
         preempt_disable();
+#  endif
+    }
     kernel_fpu_end();
 #endif
 }