/******************************************************************************

	COPYRIGHT(C) JONAS 'SORTIE' TERMANSEN 2011.

	This file is part of Sortix.

	Sortix is free software: you can redistribute it and/or modify it under the
	terms of the GNU General Public License as published by the Free Software
	Foundation, either version 3 of the License, or (at your option) any later
	version.

	Sortix is distributed in the hope that it will be useful, but WITHOUT ANY
	WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
	FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
	details.

	You should have received a copy of the GNU General Public License along
	with Sortix. If not, see <http://www.gnu.org/licenses/>.

	memorymanagement.cpp
	Handles memory for the x86 family of architectures.

******************************************************************************/

#include "platform.h"
#include <libmaxsi/memory.h>
#include "multiboot.h"
#include "panic.h"
#include "../memorymanagement.h"
#include "memorymanagement.h"

namespace Sortix
{
	const addr_t KERNELEND = 0x200000UL;

	namespace Page
	{
		void InitPushRegion(addr_t position, size_t length);
		size_t pagesnotonstack;
		size_t stackused;
		size_t stacklength;
	}

	namespace Memory
	{
		addr_t currentdir;

		void InitCPU();
		void AllocateKernelPMLs();

		void Init(multiboot_info_t* bootinfo)
		{
			Page::pagesnotonstack = 0;

			if ( !( bootinfo->flags & MULTIBOOT_INFO_MEM_MAP ) )
			{
				Panic("memorymanagement.cpp: The memory map flag was't set in "
				      "the multiboot structure. Are your bootloader multiboot "
				      "specification compliant?");
			}

			// Initialize CPU-specific things.
			InitCPU();

			typedef const multiboot_memory_map_t* mmap_t;

			// Loop over every detected memory region.
			for (
			     mmap_t mmap = (mmap_t) bootinfo->mmap_addr;
			     (addr_t) mmap < bootinfo->mmap_addr + bootinfo->mmap_length;
			     mmap = (mmap_t) ((addr_t) mmap + mmap->size + sizeof(mmap->size))
			    )
			{
				// Check that we can use this kind of RAM.
				if ( mmap->type != 1 ) { continue; }

				// The kernels code may split this memory area into multiple pieces.
				addr_t base = (addr_t) mmap->addr;
				size_t length = mmap->len;

	#ifdef PLATFORM_X86
				// Figure out if the memory area is addressable (are our pointers big enough?)
				if ( 0xFFFFFFFFULL < mmap->addr ) { continue; }
				if ( 0xFFFFFFFFULL < mmap->addr + mmap->len ) { length = 0x100000000ULL - mmap->addr;  }
	#endif

				// Detect if this memory is completely covered by the kernel.
				if ( base + length <= KERNELEND ) { continue; }

				// Detect if this memory is partially covered by the kernel.
				if ( base <= KERNELEND && KERNELEND <= base + length )
				{
					length = (base + length) - KERNELEND;
					base = KERNELEND;
				}

				Page::InitPushRegion(base, length);
			}

			// If the physical allocator couldn't handle the vast amount of
			// physical pages, it may decide to drop some. This shouldn't happen
			// until the pebibyte era of RAM.
			if ( 0 < Page::pagesnotonstack )
			{
				Log::PrintF("%zu bytes of RAM aren't used due to technical"
				            "restrictions.\n", Page::pagesnotonstack * 0x1000UL);
			}

			// Finish allocating the top level PMLs for the kernels use.
			AllocateKernelPMLs();
		}

		// Prepare the non-forkable kernel PMLs such that forking the kernel
		// address space will always keep the kernel mapped.
		void AllocateKernelPMLs()
		{
			const addr_t flags = PML_PRESENT | PML_WRITABLE;

			PML* const pml = PMLS[TOPPMLLEVEL];

			size_t start = ENTRIES / 2;
			size_t end = ENTRIES;

			for ( size_t i = start; i < end; i++ )
			{
				if ( pml->entry[i] & PML_PRESENT ) { continue; }

				addr_t page = Page::Get();
				if ( !page ) { Panic("out of memory allocating boot PMLs"); }

				pml->entry[i] = page | flags;
			}
		}
	}

	namespace Page
	{
		void ExtendStack()
		{
			// This call will always succeed, if it didn't, then the stack
			// wouldn't be full, and thus this function won't be called.
			addr_t page = Get();

			// This call will also succeed, since there are plenty of physical
			// pages available and it might need some.
			Memory::MapKernel(page, (addr_t) (STACK + stacklength));

			// TODO: This may not be needed during the boot process!
			//Memory::InvalidatePage((addr_t) (STACK + stacklength));

			stacklength += 4096UL / sizeof(addr_t);
		}

		void InitPushRegion(addr_t position, size_t length)
		{
			// Align our entries on page boundaries.
			addr_t newposition = Page::AlignUp(position);
			length = Page::AlignDown((position + length) - newposition);
			position = newposition;

			while ( length )
			{
				if ( unlikely(stackused == stacklength) )
				{
					if ( stackused == MAXSTACKLENGTH )
					{
						pagesnotonstack += length / 4096UL;
						return;
					}

					ExtendStack();
				}

				STACK[stackused++] = position;

				length -= 4096UL;
				position += 4096UL;
			}
		}

		addr_t Get()
		{
			// TODO: Set out of memory errno here!
			if ( unlikely(stackused == 0) ) { return 0; }

			return STACK[--stackused];
		}

		void Put(addr_t page)
		{
			ASSERT(stackused < MAXSTACKLENGTH);
			STACK[stackused++] = page;
		}
	}
	
	namespace Memory
	{
		void InvalidatePage(addr_t /*addr*/)
		{
			// TODO: Actually just call the instruction.
			Flush();
		}

		// Flushes the Translation Lookaside Buffer (TLB).
		void Flush()
		{
			asm volatile("mov %0, %%cr3":: "r"(currentdir));
		}

		addr_t SwitchAddressSpace(addr_t addrspace)
		{
			// Don't switch if we are already there.
			if ( addrspace == currentdir ) { return currentdir; }

			addr_t previous = currentdir;

			// Swtich and flush the TLB.
			asm volatile("mov %0, %%cr3":: "r"(addrspace));

			currentdir = addrspace;

			return previous;
		}

		bool MapRangeKernel(addr_t where, size_t bytes)
		{
			for ( addr_t page = where; page < where + bytes; page += 4096UL )
			{
				addr_t physicalpage = Page::Get();
				if ( physicalpage == 0 )
				{
					while ( where < page )
					{
						page -= 4096UL;
						physicalpage = UnmapKernel(page);
						Page::Put(physicalpage);
					}
					return false;
				}

				MapKernel(physicalpage, page);
			}

			return true;
		}

		void UnmapRangeKernel(addr_t where, size_t bytes)
		{
			for ( addr_t page = where; page < where + bytes; page += 4096UL )
			{
				addr_t physicalpage = UnmapKernel(page);
				Page::Put(physicalpage);
			}
		}

		bool MapRangeUser(addr_t where, size_t bytes)
		{
			for ( addr_t page = where; page < where + bytes; page += 4096UL )
			{
				addr_t physicalpage = Page::Get();
				if ( physicalpage == 0 || !MapUser(physicalpage, page) )
				{
					while ( where < page )
					{
						page -= 4096UL;
						physicalpage = UnmapUser(page);
						Page::Put(physicalpage);
					}
					return false;
				}
			}

			return true;
		}

		void UnmapRangeUser(addr_t where, size_t bytes)
		{
			for ( addr_t page = where; page < where + bytes; page += 4096UL )
			{
				addr_t physicalpage = UnmapUser(page);
				Page::Put(physicalpage);
			}
		}

		template <bool userspace, bool invalidate>
		bool Map(addr_t physical, addr_t mapto)
		{
			const addr_t userflags = userspace ? (PML_USERSPACE | PML_FORK) : 0;
			const addr_t flags = userflags | PML_PRESENT | PML_WRITABLE;

			const size_t MASK = (1<<TRANSBITS)-1;
			size_t pmlchildid[TOPPMLLEVEL + 1];
			for ( size_t i = 1; i <= TOPPMLLEVEL; i++ )
			{
				pmlchildid[i] = (mapto >> (12+(i-1)*TRANSBITS)) & MASK;
			}

			size_t offset = 0;
			for ( size_t i = TOPPMLLEVEL; i > 1; i-- )
			{
				size_t childid = pmlchildid[i];
				PML* pml = PMLS[i] + offset;

				addr_t& entry = pml->entry[childid];

				if ( !(entry & PML_PRESENT) )
				{
					// TODO: Possible memory leak when page allocation fails.
					addr_t page = Page::Get();
					if ( page == 0 ) { return false; }
					entry = page | flags;

					// Invalidate the new PML and reset it to zeroes.
					addr_t pmladdr = (addr_t) (PMLS[i-1] + childid);
					InvalidatePage(pmladdr);
					Maxsi::Memory::Set((void*) pmladdr, 0, sizeof(PML));
				}
				else if ( userspace && !(entry & PML_USERSPACE) )
				{
					PanicF("attempted to map physical page %p to virtual page "
					       "%p with userspace permissions, but the virtual page"
					       "wasn't in an userspace PML[%zu]. This is a bug in the"
					       "code calling this function", physical, mapto, i-1);
				}

				offset = offset * ENTRIES + childid;
			}

			(PMLS[1] + offset)->entry[pmlchildid[1]] = physical | flags;

			if ( invalidate )
			{
				InvalidatePage(mapto);
			}

			return true;
		}

		template <bool userspace, bool invalidate>
		addr_t Unmap(addr_t mapto)
		{
			const size_t MASK = (1<<TRANSBITS)-1;
			size_t pmlchildid[TOPPMLLEVEL + 1];
			for ( size_t i = 1; i <= TOPPMLLEVEL; i++ )
			{
				pmlchildid[i] = (mapto >> (12+(i-1)*TRANSBITS)) & MASK;
			}

			size_t offset = 0;
			for ( size_t i = TOPPMLLEVEL; i > 1; i-- )
			{
				size_t childid = pmlchildid[i];
				PML* pml = PMLS[i] + offset;

				addr_t& entry = pml->entry[childid];

				if ( !(entry & PML_PRESENT) )
				{
					PanicF("attempted to unmap virtual page %p with userspace, "
					       " but the virtual page wasn't mapped. This is a bug "
					       "in the code calling this function", mapto);
				}
				else if ( userspace && !(entry & PML_USERSPACE) )
				{
					PanicF("attempted to unmap virtual page %p it wasn't in an"
					       "userspace PML[%zu]. This is a bug in the code"
					       "calling this function", mapto, i-1);
				}

				offset = offset * ENTRIES + childid;
			}

			addr_t& entry = (PMLS[1] + offset)->entry[pmlchildid[1]];
			addr_t result = entry & PML_ADDRESS;
			entry = 0;

			// TODO: If all the entries in PML[N] are not-present, then who
			// unmaps its entry from PML[N-1]?

			if ( invalidate )
			{
				Flush();
			}

			return result;
		}

		bool MapKernel(addr_t physical, addr_t mapto)
		{
			return Map<false, false>(physical, mapto);
		}

		bool MapUser(addr_t physical, addr_t mapto)
		{
			return Map<true, false>(physical, mapto);
		}

		addr_t UnmapKernel(addr_t mapto)
		{
			return Unmap<false, false>(mapto);
		}

		addr_t UnmapUser(addr_t mapto)
		{
			return Unmap<true, false>(mapto);
		}

		// TODO: Copying every frame is endlessly useless in many uses. It'd be
		// nice to upgrade this to a copy-on-demand algorithm.
		addr_t Fork()
		{
			addr_t newtoppmladdr = Page::Get();
			if ( newtoppmladdr == 0 ) { return 0; }

			// This is either bad code or very clever code and probably is both.
			size_t positionstack[TOPPMLLEVEL+1];
			positionstack[TOPPMLLEVEL] = 0;
			size_t level = TOPPMLLEVEL;
			size_t pmloffset = 0;
			bool failure = false;

			// This call always succeeds.
			MapKernel(newtoppmladdr, (addr_t) (FORKPML + level));
			InvalidatePage((addr_t) (FORKPML + level));

			while ( positionstack[TOPPMLLEVEL] < ENTRIES )
			{
				const size_t pos = positionstack[level];

				if ( pos == ENTRIES )
				{
					(positionstack[++level])++;
					pmloffset /= ENTRIES;
					continue;
				}

				addr_t entry = (PMLS[level] + pmloffset)->entry[pos];

				// If the entry should be forked, fork it!
				if ( likely(entry & PML_FORK) )
				{
					// Pop the physical address of somewhere unused.
					addr_t phys = Page::Get();

					if ( unlikely(phys == 0) )
					{
						// Oh no. Out of memory! We'll have to undo everything
						// we just did. Argh!
						failure = true;
						break;
					}

					// Map the destination page.
					addr_t destaddr = (addr_t) (FORKPML + level-1);
					MapKernel(phys, destaddr);
					InvalidatePage(destaddr);

					// Set its entry in the owner.
					addr_t flags = entry & PML_FLAGS;
					(FORKPML + level)->entry[pos] = phys | flags;

					if ( level == 1 )
					{
						// Determine the source page's address.
						const void* src = (const void*) (pmloffset * 4096UL);

						// Determine the destination page's address.
						void* dest = (void*) (FORKPML + level - 1);

						Maxsi::Memory::Copy(dest, src, sizeof(PML));
					}
					else
					{
						// Fork the PML recursively!
						pmloffset = pmloffset * ENTRIES + pos;
						positionstack[--level] = 0;
						continue;
					}
				}
				
				// If this entry should be linked, link it.
				else
				{
					FORKPML[level].entry[pos] = entry;
				}

				positionstack[level]++;
			}

			if ( !failure )
			{
				// Now, the new top pml needs to have its fractal memory fixed.
				const addr_t flags = PML_PRESENT | PML_WRITABLE;
				addr_t mapto;
				addr_t childaddr;

				(FORKPML + TOPPMLLEVEL)->entry[ENTRIES-1] = newtoppmladdr | flags;
				childaddr = (FORKPML + TOPPMLLEVEL)->entry[ENTRIES-2] & PML_ADDRESS;

				for ( size_t i = TOPPMLLEVEL-1; i > 0; i-- )
				{
					mapto = (addr_t) (FORKPML + i);
					MapKernel(childaddr, mapto);
					InvalidatePage(mapto);
					(FORKPML + i)->entry[ENTRIES-1] = newtoppmladdr | flags;
					childaddr = (FORKPML + i)->entry[ENTRIES-2] & PML_ADDRESS;
				}

				return newtoppmladdr;
			}
			
			// The fork failed, so'll have to clean up the new address space and
			// free all the pages we forked so far. It'd be nice to detect that
			// this would happen early on, but it seems to impractical or
			// inefficient. Let's just do the dirty work and clean up.

			// TODO: Fix this error condition by deleting the new pages.
			Panic("Out of memory during fork. This isn't supported yet.");

			return 0;
		}
	}
}