pagetables

Documentation

Overview

Package pagetables provides a generic implementation of pagetables.

The core functions must be safe to call from a nosplit context. Furthermore, this pagetables implementation goes to lengths to ensure that all functions are free from runtime allocation. Calls to NewPTEs/FreePTEs may be made during walks, but these can be cached elsewhere if required.

Index

• type Allocator
• type MapOpts
• type PCIDs
  • func NewPCIDs(start, size uint16) *PCIDs
  • func (p *PCIDs) Assign(pt *PageTables) (uint16, bool)
  • func (p *PCIDs) Drop(pt *PageTables)
• type PTE
  • func (p *PTE) Address() uintptr
  • func (p *PTE) Clear()
  • func (p *PTE) IsSuper() bool
  • func (p *PTE) Opts() MapOpts
  • func (p *PTE) Set(addr uintptr, opts MapOpts)
  • func (p *PTE) SetSuper()
  • func (p *PTE) Valid() bool
• type PTEs
• type PageTables
  • func New(a Allocator) *PageTables
  • func NewWithUpper(a Allocator, upperSharedPageTables *PageTables, upperStart uintptr) *PageTables
  • func (p *PageTables) CR3(noFlush bool, pcid uint16) uint64
  • func (p *PageTables) Init(allocator Allocator)
  • func (p *PageTables) InitArch(allocator Allocator)
  • func (p *PageTables) IsEmpty(addr usermem.Addr, length uintptr) bool
  • func (p *PageTables) Lookup(addr usermem.Addr) (physical uintptr, opts MapOpts)
  • func (p *PageTables) Map(addr usermem.Addr, length uintptr, opts MapOpts, physical uintptr) bool
  • func (p *PageTables) MarkReadOnlyShared()
  • func (p *PageTables) Unmap(addr usermem.Addr, length uintptr) bool
• type RuntimeAllocator
  • func NewRuntimeAllocator() *RuntimeAllocator
  • func (r *RuntimeAllocator) Drain()
  • func (r *RuntimeAllocator) FreePTEs(ptes *PTEs)
  • func (r *RuntimeAllocator) Init()
  • func (r *RuntimeAllocator) LookupPTEs(physical uintptr) *PTEs
  • func (r *RuntimeAllocator) NewPTEs() *PTEs
  • func (r *RuntimeAllocator) PhysicalFor(ptes *PTEs) uintptr
  • func (r *RuntimeAllocator) Recycle()
• type Visitor
• type Walker

Types

type Allocator

type Allocator interface {
	// NewPTEs returns a new set of PTEs and their physical address.
	NewPTEs() *PTEs

	// PhysicalFor gives the physical address for a set of PTEs.
	PhysicalFor(ptes *PTEs) uintptr

	// LookupPTEs looks up PTEs by physical address.
	LookupPTEs(physical uintptr) *PTEs

	// FreePTEs marks a set of PTEs a freed, although they may not be available
	// for use again until Recycle is called, below.
	FreePTEs(ptes *PTEs)

	// Recycle makes freed PTEs available for use again.
	Recycle()
}

Allocator is used to allocate and map PTEs.

Note that allocators may be called concurrently.

type MapOpts

type MapOpts struct {
	// AccessType defines permissions.
	AccessType usermem.AccessType

	// Global indicates the page is globally accessible.
	Global bool

	// User indicates the page is a user page.
	User bool
}

MapOpts are x86 options.

type PCIDs

type PCIDs struct {
	// contains filtered or unexported fields
}

PCIDs is a simple PCID database.

This is not protected by locks and is thus suitable for use only with a single CPU at a time.

func NewPCIDs

func NewPCIDs(start, size uint16) *PCIDs

NewPCIDs returns a new PCID database.

start is the first index to assign. Typically this will be one, as the zero pcid will always be flushed on transition (see pagetables_x86.go). This may be more than one if specific PCIDs are reserved.

Nil is returned iff the start and size are out of range.

func (*PCIDs) Assign

func (p *PCIDs) Assign(pt *PageTables) (uint16, bool)

Assign assigns a PCID to the given PageTables.

This may overwrite any previous assignment provided. If this in the case, true is returned to indicate that the PCID should be flushed.

func (*PCIDs) Drop

func (p *PCIDs) Drop(pt *PageTables)

Drop drops references to a set of page tables.

type PTE

type PTE uintptr

PTE is a page table entry.

func (*PTE) Address

func (p *PTE) Address() uintptr

Address extracts the address. This should only be used if Valid returns true.

func (*PTE) Clear

func (p *PTE) Clear()

Clear clears this PTE, including super page information.

func (*PTE) IsSuper

func (p *PTE) IsSuper() bool

IsSuper returns true iff this page is a super page.

func (*PTE) Opts

func (p *PTE) Opts() MapOpts

Opts returns the PTE options.

These are all options except Valid and Super.

func (*PTE) Set

func (p *PTE) Set(addr uintptr, opts MapOpts)

Set sets this PTE value.

This does not change the super page property.

func (*PTE) SetSuper

func (p *PTE) SetSuper()

SetSuper sets this page as a super page.

The page must not be valid or a panic will result.

func (*PTE) Valid

func (p *PTE) Valid() bool

Valid returns true iff this entry is valid.

type PTEs

type PTEs [entriesPerPage]PTE

PTEs is a collection of entries.

type PageTables

type PageTables struct {
	// Allocator is used to allocate nodes.
	Allocator Allocator
	// contains filtered or unexported fields
}

PageTables is a set of page tables.

func New

func New(a Allocator) *PageTables

New returns new PageTables.

func NewWithUpper

func NewWithUpper(a Allocator, upperSharedPageTables *PageTables, upperStart uintptr) *PageTables

NewWithUpper returns new PageTables.

upperSharedPageTables are used for mapping the upper of addresses, starting at upperStart. These pageTables should not be touched (as invalidations may be incorrect) after they are passed as an upperSharedPageTables. Only when all dependent PageTables are gone may they be used. The intenteded use case is for kernel page tables, which are static and fixed.

Precondition: upperStart must be between canonical ranges. Precondition: upperStart must be pgdSize aligned. precondition: upperSharedPageTables must be marked read-only shared.

func (*PageTables) CR3

func (p *PageTables) CR3(noFlush bool, pcid uint16) uint64

CR3 returns the CR3 value for these tables.

This may be called in interrupt contexts. A PCID of zero always implies a flush and should be passed when PCIDs are not enabled. See pcids_x86.go for more information.

func (*PageTables) Init

func (p *PageTables) Init(allocator Allocator)

Init initializes a set of PageTables.

func (*PageTables) InitArch

func (p *PageTables) InitArch(allocator Allocator)

InitArch does some additional initialization related to the architecture.

func (*PageTables) IsEmpty

func (p *PageTables) IsEmpty(addr usermem.Addr, length uintptr) bool

IsEmpty checks if the given range is empty.

Precondition: addr & length must be page-aligned.

+checkescape:hard,stack

func (*PageTables) Lookup

func (p *PageTables) Lookup(addr usermem.Addr) (physical uintptr, opts MapOpts)

Lookup returns the physical address for the given virtual address.

+checkescape:hard,stack

func (*PageTables) Map

func (p *PageTables) Map(addr usermem.Addr, length uintptr, opts MapOpts, physical uintptr) bool

Map installs a mapping with the given physical address.

True is returned iff there was a previous mapping in the range.

Precondition: addr & length must be page-aligned, their sum must not overflow.

+checkescape:hard,stack

func (*PageTables) MarkReadOnlyShared

func (p *PageTables) MarkReadOnlyShared()

MarkReadOnlyShared marks the pagetables read-only and can be shared.

It is usually used on the pagetables that are used as the upper

func (*PageTables) Unmap

func (p *PageTables) Unmap(addr usermem.Addr, length uintptr) bool

Unmap unmaps the given range.

True is returned iff there was a previous mapping in the range.

Precondition: addr & length must be page-aligned, their sum must not overflow.

+checkescape:hard,stack

type RuntimeAllocator

type RuntimeAllocator struct {
	// contains filtered or unexported fields
}

RuntimeAllocator is a trivial allocator.

func NewRuntimeAllocator

func NewRuntimeAllocator() *RuntimeAllocator

NewRuntimeAllocator returns an allocator that uses runtime allocation.

func (*RuntimeAllocator) Drain

func (r *RuntimeAllocator) Drain()

Drain empties the pool.

func (*RuntimeAllocator) FreePTEs

func (r *RuntimeAllocator) FreePTEs(ptes *PTEs)

FreePTEs implements Allocator.FreePTEs.

func (*RuntimeAllocator) Init

func (r *RuntimeAllocator) Init()

Init initializes a RuntimeAllocator.

func (*RuntimeAllocator) LookupPTEs

func (r *RuntimeAllocator) LookupPTEs(physical uintptr) *PTEs

LookupPTEs implements Allocator.LookupPTEs.

func (*RuntimeAllocator) NewPTEs

func (r *RuntimeAllocator) NewPTEs() *PTEs

NewPTEs implements Allocator.NewPTEs.

Note that the "physical" address here is actually the virtual address of the PTEs structure. The entries are tracked only to avoid garbage collection.

This is guaranteed not to split as long as the pool is sufficiently full.

func (*RuntimeAllocator) PhysicalFor

func (r *RuntimeAllocator) PhysicalFor(ptes *PTEs) uintptr

PhysicalFor returns the physical address for the given PTEs.

func (*RuntimeAllocator) Recycle

func (r *RuntimeAllocator) Recycle()

Recycle returns freed pages to the pool.

type Visitor

type Visitor interface {
	// contains filtered or unexported methods
}

Visitor is a generic type.

type Walker

type Walker struct {
	// contains filtered or unexported fields
}

Walker walks page tables.