feat: power down dGPUs on hybrid graphics laptops

kernel/src/Memory/Paging.cpp

@@ -213,6 +213,10 @@ namespace Memory::VMM {
         PageTableEntry* pageEntry = (PageTableEntry*)Memory::HHDM(&PML1->entries[virtualAddressObj.GetPageIndex()]);
 
         SetLeafPte(pageEntry, physicalAddress, false, true, true);
+
+        // The page may have been mapped before with other cache attributes
+        // (an HHDM page remapped uncached): drop any stale translation.
+        asm volatile("invlpg (%0)" :: "r"(virtualAddress) : "memory");
     }
 
     void Paging::MapUser(std::uint64_t physicalAddress, std::uint64_t virtualAddress) {