gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/sentry/platform/kvm/bluepill_allocator.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package kvm
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"gvisor.dev/gvisor/pkg/ring0/pagetables"
    21  )
    22  
    23  type allocator struct {
    24  	base pagetables.RuntimeAllocator
    25  
    26  	// cpu must be set prior to any pagetable operation.
    27  	//
    28  	// Due to the way KVM's shadow paging implementation works,
    29  	// modifications to the page tables while in host mode may not be
    30  	// trapped, leading to the shadow pages being out of sync.  Therefore,
    31  	// we need to ensure that we are in guest mode for page table
    32  	// modifications. See the call to bluepill, below.
    33  	cpu *vCPU
    34  }
    35  
    36  // newAllocator is used to define the allocator.
    37  func newAllocator() *allocator {
    38  	a := new(allocator)
    39  	a.base.Init()
    40  	return a
    41  }
    42  
    43  // NewPTEs implements pagetables.Allocator.NewPTEs.
    44  //
    45  // +checkescape:all
    46  //
    47  //go:nosplit
    48  func (a *allocator) NewPTEs() *pagetables.PTEs {
    49  	ptes := a.base.NewPTEs() // escapes: bluepill below.
    50  	if a.cpu != nil {
    51  		bluepill(a.cpu)
    52  	}
    53  	return ptes
    54  }
    55  
    56  // PhysicalFor returns the physical address for a set of PTEs.
    57  //
    58  // +checkescape:all
    59  //
    60  //go:nosplit
    61  func (a *allocator) PhysicalFor(ptes *pagetables.PTEs) uintptr {
    62  	virtual := a.base.PhysicalFor(ptes)
    63  	physical, _, ok := translateToPhysical(virtual)
    64  	if !ok {
    65  		panic(fmt.Sprintf("PhysicalFor failed for %p", ptes)) // escapes: panic.
    66  	}
    67  	return physical
    68  }
    69  
    70  // LookupPTEs implements pagetables.Allocator.LookupPTEs.
    71  //
    72  // +checkescape:all
    73  //
    74  //go:nosplit
    75  func (a *allocator) LookupPTEs(physical uintptr) *pagetables.PTEs {
    76  	virtualStart, physicalStart, _, pr := calculateBluepillFault(physical, physicalRegions)
    77  	if pr == nil {
    78  		panic(fmt.Sprintf("LookupPTEs failed for 0x%x", physical)) // escapes: panic.
    79  	}
    80  	return a.base.LookupPTEs(virtualStart + (physical - physicalStart))
    81  }
    82  
    83  // FreePTEs implements pagetables.Allocator.FreePTEs.
    84  //
    85  // +checkescape:all
    86  //
    87  //go:nosplit
    88  func (a *allocator) FreePTEs(ptes *pagetables.PTEs) {
    89  	a.base.FreePTEs(ptes) // escapes: bluepill below.
    90  	if a.cpu != nil {
    91  		bluepill(a.cpu)
    92  	}
    93  }
    94  
    95  // Recycle implements pagetables.Allocator.Recycle.
    96  //
    97  //go:nosplit
    98  func (a *allocator) Recycle() {
    99  	a.base.Recycle()
   100  }