KVM: Dynamically size IPA and fault blocks on ARM64

pkg/ring0/aarch64.go

@@ -19,10 +19,16 @@ package ring0
 const (
 	// VirtualAddressBits is fixed at 48.
 	VirtualAddressBits = 48
+)
 
-	// PhysicalAddressBits is fixed at 40.
-	PhysicalAddressBits = 40
+var (
+	// PhysicalAddressBits is the number of bits available in the physical
+	// address space. On ARM64, this is dynamically limited by the host KVM IPA size,
+	// up to a maximum of 40 bits.
+	PhysicalAddressBits uintptr = 40
+)
 
+const (
 	// DAIF bits:debug, sError, IRQ, FIQ.
 	_PSR_D_BIT      = 0x00000200
 	_PSR_A_BIT      = 0x00000100

pkg/sentry/platform/kvm/kvm_amd64.go

@@ -248,6 +248,7 @@ func updateGlobalOnce(fd int) error {
 	ring0.Init(cpuid.FeatureSet{
 		Function: s,
 	})
+	initFaultBlocks()
 	physicalInit()
 	return nil
 }

pkg/sentry/platform/kvm/kvm_arm64.go

@@ -20,7 +20,9 @@ package kvm
 import (
 	"fmt"
 
+	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/hostsyscall"
 	"gvisor.dev/gvisor/pkg/ring0"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 )
@@ -66,7 +68,18 @@ type kvmVcpuEvents struct {
 // updateGlobalOnce does global initialization. It has to be called only once.
 func updateGlobalOnce(fd int) error {
 	err := updateSystemValues(int(fd))
+
+	maxIPA, errno := hostsyscall.RawSyscall(unix.SYS_IOCTL, uintptr(fd), KVM_CHECK_EXTENSION, _KVM_CAP_ARM_VM_IPA_SIZE)
+	if errno == 0 && maxIPA > 0 {
+		if maxIPA < 40 {
+			ring0.PhysicalAddressBits = uintptr(maxIPA)
+		} else {
+			ring0.PhysicalAddressBits = 40
+		}
+	}
+
 	ring0.Init()
+	initFaultBlocks()
 	physicalInit()
 
 	// Explicitly configure address space for 48-bit VA.

pkg/sentry/platform/kvm/machine.go

@@ -331,13 +331,9 @@ func newMachine(vm int, config *Config) (*machine, error) {
 	// mmap isn't called frequently, it seems better than the memory and
 	// startup time overhead introduced by mapping the entire address
 	// space.
-	mapEntireAddressSpace := forceMappingEntireAddressSpace ||
-		runtime.GOARCH != "amd64"
+	mapEntireAddressSpace := forceMappingEntireAddressSpace || mapEntireAddressSpaceDefault
 	if mapEntireAddressSpace {
-		// Increase faultBlockSize to be sure that we will not reach the limit.
-		// faultBlockSize has to equal or less than KVM_MEM_MAX_NR_PAGES.
-		faultBlockSize = uintptr(1) << 42
-		faultBlockMask = ^uintptr(faultBlockSize - 1)
+		archOverrideFaultBlocks()
 	} else {
 		// Install seccomp rules to trap runtime mmap system calls. They will
 		// be handled by seccompMmapHandler.

pkg/sentry/platform/kvm/machine_amd64.go

@@ -579,3 +579,17 @@ func (m *machine) getMaxVCPU() {
 func archPhysicalRegions(physicalRegions []physicalRegion) []physicalRegion {
 	return physicalRegions
 }
+
+const mapEntireAddressSpaceDefault = false
+
+func initFaultBlocks() {
+	faultBlockSize = uintptr(8 << 30) // 8 GiB
+	faultBlockMask = ^uintptr(faultBlockSize - 1)
+}
+
+func archOverrideFaultBlocks() {
+	// Increase faultBlockSize to be sure that we will not reach the limit.
+	// faultBlockSize has to equal or less than KVM_MEM_MAX_NR_PAGES.
+	faultBlockSize = uintptr(1) << 42
+	faultBlockMask = ^uintptr(faultBlockSize - 1)
+}

pkg/sentry/platform/kvm/machine_arm64.go

@@ -205,3 +205,16 @@ func (m *machine) getMaxVCPU() {
 		}
 	}
 }
+
+const mapEntireAddressSpaceDefault = true
+
+func initFaultBlocks() {
+	if ring0.PhysicalAddressBits <= 39 {
+		faultBlockSize = uintptr(1 << 30) // 1 GiB
+	} else {
+		faultBlockSize = uintptr(8 << 30) // 8 GiB
+	}
+	faultBlockMask = ^uintptr(faultBlockSize - 1)
+}
+
+func archOverrideFaultBlocks() {}