kvm/arm: calculate virtual-to-physical mappings only once

pkg/sentry/platform/kvm/machine.go

@@ -192,6 +192,10 @@ func (m *machine) newVCPU() *vCPU {
 	return c // Done.
 }
 
+// readOnlyGuestRegions contains regions that have to be mapped read-only into
+// the guest physical address space. Right now, it is used on arm64 only.
+var readOnlyGuestRegions []region
+
 // newMachine returns a new VM context.
 func newMachine(vm int) (*machine, error) {
 	// Create the machine.
@@ -241,32 +245,11 @@ func newMachine(vm int) (*machine, error) {
 		return true // Keep iterating.
 	})
 
-	var physicalRegionsReadOnly []physicalRegion
-	var physicalRegionsAvailable []physicalRegion
-
-	physicalRegionsReadOnly = rdonlyRegionsForSetMem()
-	physicalRegionsAvailable = availableRegionsForSetMem()
-
-	// Map all read-only regions.
-	for _, r := range physicalRegionsReadOnly {
-		m.mapPhysical(r.physical, r.length, physicalRegionsReadOnly, _KVM_MEM_READONLY)
-	}
-
 	// Ensure that the currently mapped virtual regions are actually
 	// available in the VM. Note that this doesn't guarantee no future
 	// faults, however it should guarantee that everything is available to
 	// ensure successful vCPU entry.
-	applyVirtualRegions(func(vr virtualRegion) {
-		if excludeVirtualRegion(vr) {
-			return // skip region.
-		}
-
-		for _, r := range physicalRegionsReadOnly {
-			if vr.virtual == r.virtual {
-				return
-			}
-		}
-
+	mapRegion := func(vr region, flags uint32) {
 		for virtual := vr.virtual; virtual < vr.virtual+vr.length; {
 			physical, length, ok := translateToPhysical(virtual)
 			if !ok {
@@ -280,9 +263,26 @@ func newMachine(vm int) (*machine, error) {
 			}
 
 			// Ensure the physical range is mapped.
-			m.mapPhysical(physical, length, physicalRegionsAvailable, _KVM_MEM_FLAGS_NONE)
+			m.mapPhysical(physical, length, physicalRegions, flags)
 			virtual += length
 		}
+	}
+
+	for _, vr := range(readOnlyGuestRegions) {
+		mapRegion(vr, _KVM_MEM_READONLY)
+	}
+
+	applyVirtualRegions(func(vr virtualRegion) {
+		if excludeVirtualRegion(vr) {
+			return // skip region.
+		}
+		for _, r := range readOnlyGuestRegions {
+			if vr.virtual == r.virtual {
+				return
+			}
+		}
+		mapRegion(vr.region, 0)
+
 	})
 
 	// Initialize architecture state.

pkg/sentry/platform/kvm/machine_amd64.go

@@ -522,3 +522,7 @@ func (m *machine) getNewVCPU() *vCPU {
 	}
 	return nil
 }
+
+func archPhysicalRegions(physicalRegions []physicalRegion) ([]physicalRegion) {
+	return physicalRegions
+}

pkg/sentry/platform/kvm/machine_arm64.go

@@ -110,18 +110,128 @@ func rdonlyRegionsForSetMem() (phyRegions []physicalRegion) {
 	return phyRegions
 }
 
-// Get all available physicalRegions.
-func availableRegionsForSetMem() (phyRegions []physicalRegion) {
-	var excludeRegions []region
+// archPhysicalRegions fills readOnlyGuestRegions and allocates separate
+// physical regions form them.
+func archPhysicalRegions(physicalRegions []physicalRegion) ([]physicalRegion) {
 	applyVirtualRegions(func(vr virtualRegion) {
+		if excludeVirtualRegion(vr) {
+			return // skip region.
+		}
 		if !vr.accessType.Write {
-			excludeRegions = append(excludeRegions, vr.region)
+			readOnlyGuestRegions = append(readOnlyGuestRegions, vr.region)
 		}
 	})
 
-	phyRegions = computePhysicalRegions(excludeRegions)
+	rdRegions := readOnlyGuestRegions[:]
 
-	return phyRegions
+	// Add an unreachable region.
+	rdRegions = append(rdRegions, region {
+		virtual: 0xffffffffffffffff,
+		length: 0,
+	})
+
+	var regions  []physicalRegion
+	addValidRegion := func(r *physicalRegion, virtual, length uintptr) {
+		if length == 0 {
+			return
+		}
+		regions = append(regions, physicalRegion {
+				region: region{
+					virtual: virtual,
+					length: length,
+				},
+				physical: r.physical + (virtual - r.virtual),
+		})
+	}
+	i := 0
+	for _, pr := range(physicalRegions) {
+		start := pr.virtual
+		end := pr.virtual + pr.length
+		for start < end {
+			rdRegion := rdRegions[i]
+			rdStart := rdRegion.virtual
+			rdEnd := rdRegion.virtual + rdRegion.length
+			if rdEnd <= start {
+				i++
+				continue
+			}
+			if rdStart > start {
+				newEnd := rdStart
+				if end < rdStart {
+					newEnd = end
+				}
+				addValidRegion(&pr, start, newEnd - start)
+				start = rdStart
+				continue
+			}
+			if rdEnd < end {
+				addValidRegion(&pr, start, rdEnd - start)
+				start = rdEnd
+				continue
+			}
+			addValidRegion(&pr, start, end - start)
+			start = end
+		}
+	}
+
+	return regions
+}
+
+// Get all available physicalRegions.
+func availableRegionsForSetMem() ([]physicalRegion) {
+	var excludedRegions []region
+	applyVirtualRegions(func(vr virtualRegion) {
+		if !vr.accessType.Write {
+			excludedRegions = append(excludedRegions, vr.region)
+		}
+	})
+
+	// Add an unreachable region.
+	excludedRegions = append(excludedRegions, region {
+		virtual: 0xffffffffffffffff,
+		length: 0,
+	})
+
+	var regions []physicalRegion
+	addValidRegion := func(r *physicalRegion, virtual, length uintptr) {
+		if length == 0 {
+			return
+		}
+		regions = append(regions, physicalRegion {
+				region: region{
+					virtual: virtual,
+					length: length,
+				},
+				physical: r.physical + (virtual - r.virtual),
+		})
+	}
+	i := 0
+	for _, pr := range(physicalRegions) {
+		start := pr.virtual
+		end := pr.virtual + pr.length
+		for start < end {
+			er := excludedRegions[i]
+			excludeEnd := er.virtual + er.length
+			excludeStart := er.virtual
+			if excludeEnd < start {
+				i++
+				continue
+			}
+			if excludeStart < start {
+				start = excludeEnd
+				i++
+				continue
+			}
+			rend := excludeStart
+			if rend > end {
+				rend = end
+			}
+			addValidRegion(&pr, start, rend - start)
+			start = excludeEnd
+		}
+	}
+
+	return regions
 }
 
 // nonCanonical generates a canonical address return.

pkg/sentry/platform/kvm/physical_map.go

@@ -168,6 +168,9 @@ func computePhysicalRegions(excludedRegions []region) (physicalRegions []physica
 	}
 	addValidRegion(lastExcludedEnd, ring0.MaximumUserAddress-lastExcludedEnd)
 
+	// Do arch-specific actions on physical regions.
+	physicalRegions = archPhysicalRegions(physicalRegions)
+
 	// Dump our all physical regions.
 	for _, r := range physicalRegions {
 		log.Infof("physicalRegion: virtual [%x,%x) => physical [%x,%x)",