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Implement COW pages! :^)

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sys$fork() now clones all writable regions with per-page COW bits.
The pages are then mapped read-only and we handle a PF by COWing the pages.

This is quite delightful. Obviously there's lots of work to do still,
and it needs better data structures, but the general concept works.
This commit is contained in:
Andreas Kling 2018-11-05 13:48:07 +01:00
parent e85c22fe58
commit 2d045d2a64
11 changed files with 271 additions and 97 deletions
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24
Kernel/MemoryManager.h
View file

@ -2,6 +2,7 @@
#include "types.h"
#include "i386.h"
#include <AK/Bitmap.h>
#include <AK/ByteBuffer.h>
#include <AK/Retainable.h>
#include <AK/RetainPtr.h>
@ -54,16 +55,27 @@ struct PageDirectory {
};
struct Region : public Retainable<Region> {
Region(LinearAddress, size_t, Vector<RetainPtr<PhysicalPage>>, String&&, bool r, bool w);
Region(LinearAddress, size_t, Vector<RetainPtr<PhysicalPage>>, String&&, bool r, bool w, bool cow = false);
~Region();
RetainPtr<Region> clone();
bool contains(LinearAddress laddr) const
{
return laddr >= linearAddress && laddr < linearAddress.offset(size);
}
unsigned page_index_from_address(LinearAddress laddr) const
{
return (laddr - linearAddress).get() / PAGE_SIZE;
}
LinearAddress linearAddress;
size_t size { 0 };
Vector<RetainPtr<PhysicalPage>> physical_pages;
String name;
bool is_readable { true };
bool is_writable { true };
Bitmap cow_map;
};
#define MM MemoryManager::the()
@ -98,6 +110,8 @@ public:
Vector<RetainPtr<PhysicalPage>> allocate_physical_pages(size_t count);
void remap_region(Process&, Region&);
private:
MemoryManager();
~MemoryManager();
@ -105,6 +119,7 @@ private:
LinearAddress allocate_linear_address_range(size_t);
void map_region_at_address(PageDirectory*, Region&, LinearAddress, bool user_accessible);
void unmap_range(PageDirectory*, LinearAddress, size_t);
void remap_region_page(PageDirectory*, Region&, unsigned page_index_in_region, bool user_allowed);
void initializePaging();
void flushEntireTLB();
@ -118,6 +133,13 @@ private:
void create_identity_mapping(LinearAddress, size_t length);
void remove_identity_mapping(LinearAddress, size_t);
static Region* region_from_laddr(Process&, LinearAddress);
bool copy_on_write(Process&, Region&, unsigned page_index_in_region);
byte* quickmap_page(PhysicalPage&);
void unquickmap_page();
struct PageDirectoryEntry {
explicit PageDirectoryEntry(dword* pde) : m_pde(pde) { }