105 lines
2.7 KiB
Go
105 lines
2.7 KiB
Go
// Copyright 2018 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package pagetables
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import (
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"gvisor.dev/gvisor/pkg/sync"
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)
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// PCIDs is a simple PCID database.
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//
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// This is not protected by locks and is thus suitable for use only with a
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// single CPU at a time.
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type PCIDs struct {
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// mu protects below.
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mu sync.Mutex
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// cache are the assigned page tables.
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cache map[*PageTables]uint16
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// avail are available PCIDs.
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avail []uint16
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}
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// NewPCIDs returns a new PCID database.
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//
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// start is the first index to assign. Typically this will be one, as the zero
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// pcid will always be flushed on transition (see pagetables_x86.go). This may
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// be more than one if specific PCIDs are reserved.
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//
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// Nil is returned iff the start and size are out of range.
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func NewPCIDs(start, size uint16) *PCIDs {
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if start+uint16(size) > limitPCID {
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return nil // See comment.
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}
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p := &PCIDs{
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cache: make(map[*PageTables]uint16),
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}
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for pcid := start; pcid < start+size; pcid++ {
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p.avail = append(p.avail, pcid)
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}
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return p
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}
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// Assign assigns a PCID to the given PageTables.
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//
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// This may overwrite any previous assignment provided. If this in the case,
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// true is returned to indicate that the PCID should be flushed.
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func (p *PCIDs) Assign(pt *PageTables) (uint16, bool) {
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p.mu.Lock()
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if pcid, ok := p.cache[pt]; ok {
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p.mu.Unlock()
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return pcid, false // No flush.
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}
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// Is there something available?
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if len(p.avail) > 0 {
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pcid := p.avail[len(p.avail)-1]
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p.avail = p.avail[:len(p.avail)-1]
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p.cache[pt] = pcid
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// We need to flush because while this is in the available
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// pool, it may have been used previously.
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p.mu.Unlock()
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return pcid, true
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}
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// Evict an existing table.
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for old, pcid := range p.cache {
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delete(p.cache, old)
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p.cache[pt] = pcid
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// A flush is definitely required in this case, these page
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// tables may still be active. (They will just be assigned some
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// other PCID if and when they hit the given CPU again.)
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p.mu.Unlock()
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return pcid, true
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}
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// No PCID.
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p.mu.Unlock()
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return 0, false
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}
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// Drop drops references to a set of page tables.
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func (p *PCIDs) Drop(pt *PageTables) {
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p.mu.Lock()
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if pcid, ok := p.cache[pt]; ok {
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delete(p.cache, pt)
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p.avail = append(p.avail, pcid)
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}
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p.mu.Unlock()
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}
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