Merge release-20200323.0-49-g4e6a1a5 (automated)

13 files changed, 118 insertions, 149 deletions

diff --git a/pkg/atomicbitops/atomicbitops_amd64.s b/pkg/atomicbitops/atomicbitops_amd64.s
index f0edd4de7..54c887ee5 100755
--- a/pkg/atomicbitops/atomicbitops_amd64.s
+++ b/pkg/atomicbitops/atomicbitops_amd64.s
@@ -16,28 +16,28 @@
 
 #include "textflag.h"
 
-TEXT ·AndUint32(SB),NOSPLIT,$0-12
+TEXT ·AndUint32(SB),$0-12
   MOVQ  addr+0(FP), BP
   MOVL  val+8(FP), AX
   LOCK
   ANDL   AX, 0(BP)
   RET
 
-TEXT ·OrUint32(SB),NOSPLIT,$0-12
+TEXT ·OrUint32(SB),$0-12
   MOVQ  addr+0(FP), BP
   MOVL  val+8(FP), AX
   LOCK
   ORL   AX, 0(BP)
   RET
 
-TEXT ·XorUint32(SB),NOSPLIT,$0-12
+TEXT ·XorUint32(SB),$0-12
   MOVQ  addr+0(FP), BP
   MOVL  val+8(FP), AX
   LOCK
   XORL   AX, 0(BP)
   RET
 
-TEXT ·CompareAndSwapUint32(SB),NOSPLIT,$0-20
+TEXT ·CompareAndSwapUint32(SB),$0-20
   MOVQ  addr+0(FP), DI
   MOVL  old+8(FP), AX
   MOVL  new+12(FP), DX
@@ -46,28 +46,28 @@ TEXT ·CompareAndSwapUint32(SB),NOSPLIT,$0-20
   MOVL  AX, ret+16(FP)
   RET
 
-TEXT ·AndUint64(SB),NOSPLIT,$0-16
+TEXT ·AndUint64(SB),$0-16
   MOVQ  addr+0(FP), BP
   MOVQ  val+8(FP), AX
   LOCK
   ANDQ   AX, 0(BP)
   RET
 
-TEXT ·OrUint64(SB),NOSPLIT,$0-16
+TEXT ·OrUint64(SB),$0-16
   MOVQ  addr+0(FP), BP
   MOVQ  val+8(FP), AX
   LOCK
   ORQ   AX, 0(BP)
   RET
 
-TEXT ·XorUint64(SB),NOSPLIT,$0-16
+TEXT ·XorUint64(SB),$0-16
   MOVQ  addr+0(FP), BP
   MOVQ  val+8(FP), AX
   LOCK
   XORQ   AX, 0(BP)
   RET
 
-TEXT ·CompareAndSwapUint64(SB),NOSPLIT,$0-32
+TEXT ·CompareAndSwapUint64(SB),$0-32
   MOVQ  addr+0(FP), DI
   MOVQ  old+8(FP), AX
   MOVQ  new+16(FP), DX
diff --git a/pkg/atomicbitops/atomicbitops_arm64.s b/pkg/atomicbitops/atomicbitops_arm64.s
index 644a6bca5..5c780851b 100755
--- a/pkg/atomicbitops/atomicbitops_arm64.s
+++ b/pkg/atomicbitops/atomicbitops_arm64.s
@@ -16,7 +16,7 @@
 
 #include "textflag.h"
 
-TEXT ·AndUint32(SB),NOSPLIT,$0-12
+TEXT ·AndUint32(SB),$0-12
   MOVD    ptr+0(FP), R0
   MOVW    val+8(FP), R1
 again:
@@ -26,7 +26,7 @@ again:
   CBNZ    R3, again
   RET
 
-TEXT ·OrUint32(SB),NOSPLIT,$0-12
+TEXT ·OrUint32(SB),$0-12
   MOVD    ptr+0(FP), R0
   MOVW    val+8(FP), R1
 again:
@@ -36,7 +36,7 @@ again:
   CBNZ    R3, again
   RET
 
-TEXT ·XorUint32(SB),NOSPLIT,$0-12
+TEXT ·XorUint32(SB),$0-12
   MOVD    ptr+0(FP), R0
   MOVW    val+8(FP), R1
 again:
@@ -46,7 +46,7 @@ again:
   CBNZ    R3, again
   RET
 
-TEXT ·CompareAndSwapUint32(SB),NOSPLIT,$0-20
+TEXT ·CompareAndSwapUint32(SB),$0-20
   MOVD addr+0(FP), R0
   MOVW old+8(FP), R1
   MOVW new+12(FP), R2
@@ -60,7 +60,7 @@ done:
   MOVW R3, prev+16(FP)
   RET
 
-TEXT ·AndUint64(SB),NOSPLIT,$0-16
+TEXT ·AndUint64(SB),$0-16
   MOVD    ptr+0(FP), R0
   MOVD    val+8(FP), R1
 again:
@@ -70,7 +70,7 @@ again:
   CBNZ    R3, again
   RET
 
-TEXT ·OrUint64(SB),NOSPLIT,$0-16
+TEXT ·OrUint64(SB),$0-16
   MOVD    ptr+0(FP), R0
   MOVD    val+8(FP), R1
 again:
@@ -80,7 +80,7 @@ again:
   CBNZ    R3, again
   RET
 
-TEXT ·XorUint64(SB),NOSPLIT,$0-16
+TEXT ·XorUint64(SB),$0-16
   MOVD    ptr+0(FP), R0
   MOVD    val+8(FP), R1
 again:
@@ -90,7 +90,7 @@ again:
   CBNZ    R3, again
   RET
 
-TEXT ·CompareAndSwapUint64(SB),NOSPLIT,$0-32
+TEXT ·CompareAndSwapUint64(SB),$0-32
   MOVD addr+0(FP), R0
   MOVD old+8(FP), R1
   MOVD new+16(FP), R2
diff --git a/pkg/atomicbitops/atomicbitops_noasm.go b/pkg/atomicbitops/atomicbitops_noasm.go
index 4e9c27b98..3b2898256 100755
--- a/pkg/atomicbitops/atomicbitops_noasm.go
+++ b/pkg/atomicbitops/atomicbitops_noasm.go
@@ -20,7 +20,6 @@ import (
 	"sync/atomic"
 )
 
-//go:nosplit
 func AndUint32(addr *uint32, val uint32) {
 	for {
 		o := atomic.LoadUint32(addr)
@@ -31,7 +30,6 @@ func AndUint32(addr *uint32, val uint32) {
 	}
 }
 
-//go:nosplit
 func OrUint32(addr *uint32, val uint32) {
 	for {
 		o := atomic.LoadUint32(addr)
@@ -42,7 +40,6 @@ func OrUint32(addr *uint32, val uint32) {
 	}
 }
 
-//go:nosplit
 func XorUint32(addr *uint32, val uint32) {
 	for {
 		o := atomic.LoadUint32(addr)
@@ -53,7 +50,6 @@ func XorUint32(addr *uint32, val uint32) {
 	}
 }
 
-//go:nosplit
 func CompareAndSwapUint32(addr *uint32, old, new uint32) (prev uint32) {
 	for {
 		prev = atomic.LoadUint32(addr)
@@ -66,7 +62,6 @@ func CompareAndSwapUint32(addr *uint32, old, new uint32) (prev uint32) {
 	}
 }
 
-//go:nosplit
 func AndUint64(addr *uint64, val uint64) {
 	for {
 		o := atomic.LoadUint64(addr)
@@ -77,7 +72,6 @@ func AndUint64(addr *uint64, val uint64) {
 	}
 }
 
-//go:nosplit
 func OrUint64(addr *uint64, val uint64) {
 	for {
 		o := atomic.LoadUint64(addr)
@@ -88,7 +82,6 @@ func OrUint64(addr *uint64, val uint64) {
 	}
 }
 
-//go:nosplit
 func XorUint64(addr *uint64, val uint64) {
 	for {
 		o := atomic.LoadUint64(addr)
@@ -99,7 +92,6 @@ func XorUint64(addr *uint64, val uint64) {
 	}
 }
 
-//go:nosplit
 func CompareAndSwapUint64(addr *uint64, old, new uint64) (prev uint64) {
 	for {
 		prev = atomic.LoadUint64(addr)
diff --git a/pkg/safecopy/safecopy.go b/pkg/safecopy/safecopy.go
index 521f1a82d..2fb7e5809 100755
--- a/pkg/safecopy/safecopy.go
+++ b/pkg/safecopy/safecopy.go
@@ -127,10 +127,10 @@ func initializeAddresses() {
 
 func init() {
 	initializeAddresses()
-	if err := ReplaceSignalHandler(syscall.SIGSEGV, reflect.ValueOf(signalHandler).Pointer(), &savedSigSegVHandler, 0); err != nil {
+	if err := ReplaceSignalHandler(syscall.SIGSEGV, reflect.ValueOf(signalHandler).Pointer(), &savedSigSegVHandler); err != nil {
 		panic(fmt.Sprintf("Unable to set handler for SIGSEGV: %v", err))
 	}
-	if err := ReplaceSignalHandler(syscall.SIGBUS, reflect.ValueOf(signalHandler).Pointer(), &savedSigBusHandler, 0); err != nil {
+	if err := ReplaceSignalHandler(syscall.SIGBUS, reflect.ValueOf(signalHandler).Pointer(), &savedSigBusHandler); err != nil {
 		panic(fmt.Sprintf("Unable to set handler for SIGBUS: %v", err))
 	}
 	syserror.AddErrorUnwrapper(func(e error) (syscall.Errno, bool) {
diff --git a/pkg/safecopy/safecopy_unsafe.go b/pkg/safecopy/safecopy_unsafe.go
index b15b920fe..41dd567f3 100755
--- a/pkg/safecopy/safecopy_unsafe.go
+++ b/pkg/safecopy/safecopy_unsafe.go
@@ -324,13 +324,11 @@ func errorFromFaultSignal(addr uintptr, sig int32) error {
 //
 // It stores the value of the previously set handler in previous.
 //
-// The extraMask parameter is OR'ed into the existing signal handler mask.
-//
 // This function will be called on initialization in order to install safecopy
 // handlers for appropriate signals. These handlers will call the previous
 // handler however, and if this is function is being used externally then the
 // same courtesy is expected.
-func ReplaceSignalHandler(sig syscall.Signal, handler uintptr, previous *uintptr, extraMask uint64) error {
+func ReplaceSignalHandler(sig syscall.Signal, handler uintptr, previous *uintptr) error {
 	var sa struct {
 		handler  uintptr
 		flags    uint64
@@ -350,10 +348,10 @@ func ReplaceSignalHandler(sig syscall.Signal, handler uintptr, previous *uintptr
 	if sa.handler == 0 {
 		return fmt.Errorf("previous handler for signal %x isn't set", sig)
 	}
+
 	*previous = sa.handler
 
 	// Install our own handler.
-	sa.mask |= extraMask
 	sa.handler = handler
 	if _, _, e := syscall.RawSyscall6(syscall.SYS_RT_SIGACTION, uintptr(sig), uintptr(unsafe.Pointer(&sa)), 0, maskLen, 0, 0); e != 0 {
 		return e
diff --git a/pkg/sentry/platform/kvm/bluepill.go b/pkg/sentry/platform/kvm/bluepill.go
index 555b5fa96..4b23f7803 100644
--- a/pkg/sentry/platform/kvm/bluepill.go
+++ b/pkg/sentry/platform/kvm/bluepill.go
@@ -46,14 +46,6 @@ var (
 	// bounceSignalMask has only bounceSignal set.
 	bounceSignalMask = uint64(1 << (uint64(bounceSignal) - 1))
 
-	// otherSignalsMask includes all other signals that will be cause the
-	// vCPU to exit during execution.
-	//
-	// Currently, this includes the preemption signal and the profiling
-	// signal. In general, these should be signals whose delivery actually
-	// influences the way the program executes as the switch can be costly.
-	otherSignalsMask = uint64(1<<(uint64(syscall.SIGURG)-1)) | uint64(1<<(uint64(syscall.SIGPROF)-1))
-
 	// bounce is the interrupt vector used to return to the kernel.
 	bounce = uint32(ring0.VirtualizationException)
 
@@ -94,8 +86,8 @@ func (c *vCPU) die(context *arch.SignalContext64, msg string) {
 }
 
 func init() {
-	// Install the handler, masking all signals.
-	if err := safecopy.ReplaceSignalHandler(bluepillSignal, reflect.ValueOf(sighandler).Pointer(), &savedHandler, ^uint64(0)); err != nil {
+	// Install the handler.
+	if err := safecopy.ReplaceSignalHandler(bluepillSignal, reflect.ValueOf(sighandler).Pointer(), &savedHandler); err != nil {
 		panic(fmt.Sprintf("Unable to set handler for signal %d: %v", bluepillSignal, err))
 	}
 
diff --git a/pkg/sentry/platform/kvm/bluepill_unsafe.go b/pkg/sentry/platform/kvm/bluepill_unsafe.go
index 4e9d80765..9add7c944 100644
--- a/pkg/sentry/platform/kvm/bluepill_unsafe.go
+++ b/pkg/sentry/platform/kvm/bluepill_unsafe.go
@@ -24,7 +24,6 @@ import (
 	"syscall"
 	"unsafe"
 
-	"gvisor.dev/gvisor/pkg/atomicbitops"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 )
 
@@ -59,19 +58,6 @@ func bluepillArchContext(context unsafe.Pointer) *arch.SignalContext64 {
 	return &((*arch.UContext64)(context).MContext)
 }
 
-// injectInterrupt is a helper to inject an interrupt.
-//
-//go:nosplit
-func injectInterrupt(c *vCPU) {
-	if _, _, errno := syscall.RawSyscall(
-		syscall.SYS_IOCTL,
-		uintptr(c.fd),
-		_KVM_INTERRUPT,
-		uintptr(unsafe.Pointer(&bounce))); errno != 0 {
-		throw("interrupt injection failed")
-	}
-}
-
 // bluepillHandler is called from the signal stub.
 //
 // The world may be stopped while this is executing, and it executes on the
@@ -83,9 +69,6 @@ func bluepillHandler(context unsafe.Pointer) {
 	// Sanitize the registers; interrupts must always be disabled.
 	c := bluepillArchEnter(bluepillArchContext(context))
 
-	// Enable preemption.
-	c.setSignalMask(true)
-
 	// Increment the number of switches.
 	atomic.AddUint32(&c.switches, 1)
 
@@ -106,9 +89,6 @@ func bluepillHandler(context unsafe.Pointer) {
 			// interrupted KVM. Since we're in a signal handler
 			// currently, all signals are masked and the signal
 			// must have been delivered directly to this thread.
-			//
-			// We will not be able to actually do subsequent
-			// KVM_RUNs until this signal is processed.
 			timeout := syscall.Timespec{}
 			sig, _, errno := syscall.RawSyscall6(
 				syscall.SYS_RT_SIGTIMEDWAIT,
@@ -118,24 +98,12 @@ func bluepillHandler(context unsafe.Pointer) {
 				8,                                 // sigset size.
 				0, 0)
 			if errno == syscall.EAGAIN {
-				// If weren't able to process this signal, then
-				// it must not have been in the bounceMask. By
-				// elimination, it must have been the
-				// preemption signal. We can't process this
-				// signal right now, so we need to disable
-				// preemption until the interrupt is actually
-				// handled.
-				c.setSignalMask(false)
-				// Note that there is a waiter for this vCPU.
-				// This will cause the vCPU to exit at some
-				// point in the future (releasing the user lock
-				// and guest mode).
-				atomicbitops.OrUint32(&c.state, vCPUWaiter)
-			} else if errno != 0 {
-				// We only expect success or a timeout.
+				continue
+			}
+			if errno != 0 {
 				throw("error waiting for pending signal")
-			} else if sig != uintptr(bounceSignal) {
-				// Only the bounce should be processed.
+			}
+			if sig != uintptr(bounceSignal) {
 				throw("unexpected signal")
 			}
 
@@ -146,10 +114,11 @@ func bluepillHandler(context unsafe.Pointer) {
 			// ready.
 			if c.runData.readyForInterruptInjection == 0 {
 				c.runData.requestInterruptWindow = 1
+				continue // Rerun vCPU.
 			} else {
-				injectInterrupt(c)
+				// Force injection below; the vCPU is ready.
+				c.runData.exitReason = _KVM_EXIT_IRQ_WINDOW_OPEN
 			}
-			continue // Rerun vCPU.
 		case syscall.EFAULT:
 			// If a fault is not serviceable due to the host
 			// backing pages having page permissions, instead of an
@@ -168,30 +137,6 @@ func bluepillHandler(context unsafe.Pointer) {
 		}
 
 		switch c.runData.exitReason {
-		case _KVM_EXIT_HLT:
-			// Copy out registers.
-			bluepillArchExit(c, bluepillArchContext(context))
-
-			// Return to the vCPUReady state; notify any waiters.
-			user := atomic.LoadUint32(&c.state) & vCPUUser
-			switch atomic.SwapUint32(&c.state, user) {
-			case user | vCPUGuest: // Expected case.
-			case user | vCPUGuest | vCPUWaiter:
-				c.notify()
-			default:
-				throw("invalid state")
-			}
-			return
-		case _KVM_EXIT_IRQ_WINDOW_OPEN:
-			// Inject an interrupt now.
-			injectInterrupt(c)
-			// Clear previous injection request.
-			c.runData.requestInterruptWindow = 0
-		case _KVM_EXIT_INTR:
-			// This is fine, it is the normal exit reason during
-			// signal delivery. However, we still need to handle
-			// other potential exit reasons *combined* with EINTR,
-			// so this switch must be hit even after the above.
 		case _KVM_EXIT_EXCEPTION:
 			c.die(bluepillArchContext(context), "exception")
 			return
@@ -210,6 +155,20 @@ func bluepillHandler(context unsafe.Pointer) {
 		case _KVM_EXIT_DEBUG:
 			c.die(bluepillArchContext(context), "debug")
 			return
+		case _KVM_EXIT_HLT:
+			// Copy out registers.
+			bluepillArchExit(c, bluepillArchContext(context))
+
+			// Return to the vCPUReady state; notify any waiters.
+			user := atomic.LoadUint32(&c.state) & vCPUUser
+			switch atomic.SwapUint32(&c.state, user) {
+			case user | vCPUGuest: // Expected case.
+			case user | vCPUGuest | vCPUWaiter:
+				c.notify()
+			default:
+				throw("invalid state")
+			}
+			return
 		case _KVM_EXIT_MMIO:
 			// Increment the fault count.
 			atomic.AddUint32(&c.faults, 1)
@@ -241,6 +200,18 @@ func bluepillHandler(context unsafe.Pointer) {
 					data[i] = *b
 				}
 			}
+		case _KVM_EXIT_IRQ_WINDOW_OPEN:
+			// Interrupt: we must have requested an interrupt
+			// window; set the interrupt line.
+			if _, _, errno := syscall.RawSyscall(
+				syscall.SYS_IOCTL,
+				uintptr(c.fd),
+				_KVM_INTERRUPT,
+				uintptr(unsafe.Pointer(&bounce))); errno != 0 {
+				throw("interrupt injection failed")
+			}
+			// Clear previous injection request.
+			c.runData.requestInterruptWindow = 0
 		case _KVM_EXIT_SHUTDOWN:
 			c.die(bluepillArchContext(context), "shutdown")
 			return
diff --git a/pkg/sentry/platform/kvm/kvm_const.go b/pkg/sentry/platform/kvm/kvm_const.go
index 07d9c9a98..1d5c77ff4 100644
--- a/pkg/sentry/platform/kvm/kvm_const.go
+++ b/pkg/sentry/platform/kvm/kvm_const.go
@@ -48,7 +48,6 @@ const (
 	_KVM_EXIT_IRQ_WINDOW_OPEN = 0x7
 	_KVM_EXIT_SHUTDOWN        = 0x8
 	_KVM_EXIT_FAIL_ENTRY      = 0x9
-	_KVM_EXIT_INTR            = 0xa
 	_KVM_EXIT_INTERNAL_ERROR  = 0x11
 	_KVM_EXIT_SYSTEM_EVENT    = 0x18
 )
diff --git a/pkg/sentry/platform/kvm/machine.go b/pkg/sentry/platform/kvm/machine.go
index 345b71e8f..f1afc74dc 100644
--- a/pkg/sentry/platform/kvm/machine.go
+++ b/pkg/sentry/platform/kvm/machine.go
@@ -108,9 +108,6 @@ type vCPU struct {
 	// This is a bitmask of the three fields (vCPU*) described above.
 	state uint32
 
-	// signalMask is the vCPU signal mask.
-	signalMask uint64
-
 	// runData for this vCPU.
 	runData *runData
 
@@ -124,7 +121,6 @@ type vCPU struct {
 	// vCPUArchState is the architecture-specific state.
 	vCPUArchState
 
-	// dieState is the temporary state associated with throwing exceptions.
 	dieState dieState
 }
 
@@ -157,6 +153,11 @@ func (m *machine) newVCPU() *vCPU {
 	c.CPU.Init(&m.kernel, c)
 	m.vCPUsByID[c.id] = c
 
+	// Ensure the signal mask is correct.
+	if err := c.setSignalMask(); err != nil {
+		panic(fmt.Sprintf("error setting signal mask: %v", err))
+	}
+
 	// Map the run data.
 	runData, err := mapRunData(int(fd))
 	if err != nil {
diff --git a/pkg/sentry/platform/kvm/machine_amd64_unsafe.go b/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
index 52286e56d..7156c245f 100644
--- a/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
@@ -111,6 +111,31 @@ func (c *vCPU) setSystemTime() error {
 	return nil
 }
 
+// setSignalMask sets the vCPU signal mask.
+//
+// This must be called prior to running the vCPU.
+func (c *vCPU) setSignalMask() error {
+	// The layout of this structure implies that it will not necessarily be
+	// the same layout chosen by the Go compiler. It gets fudged here.
+	var data struct {
+		length uint32
+		mask1  uint32
+		mask2  uint32
+		_      uint32
+	}
+	data.length = 8 // Fixed sigset size.
+	data.mask1 = ^uint32(bounceSignalMask & 0xffffffff)
+	data.mask2 = ^uint32(bounceSignalMask >> 32)
+	if _, _, errno := syscall.RawSyscall(
+		syscall.SYS_IOCTL,
+		uintptr(c.fd),
+		_KVM_SET_SIGNAL_MASK,
+		uintptr(unsafe.Pointer(&data))); errno != 0 {
+		return fmt.Errorf("error setting signal mask: %v", errno)
+	}
+	return nil
+}
+
 // setUserRegisters sets user registers in the vCPU.
 func (c *vCPU) setUserRegisters(uregs *userRegs) error {
 	if _, _, errno := syscall.RawSyscall(
diff --git a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
index 185eeb4f0..b531f2f85 100755
--- a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
@@ -268,6 +268,32 @@ func (c *vCPU) setSystemTime() error {
 	return nil
 }
 
+// setSignalMask sets the vCPU signal mask.
+//
+// This must be called prior to running the vCPU.
+func (c *vCPU) setSignalMask() error {
+	// The layout of this structure implies that it will not necessarily be
+	// the same layout chosen by the Go compiler. It gets fudged here.
+	var data struct {
+		length uint32
+		mask1  uint32
+		mask2  uint32
+		_      uint32
+	}
+	data.length = 8 // Fixed sigset size.
+	data.mask1 = ^uint32(bounceSignalMask & 0xffffffff)
+	data.mask2 = ^uint32(bounceSignalMask >> 32)
+	if _, _, errno := syscall.RawSyscall(
+		syscall.SYS_IOCTL,
+		uintptr(c.fd),
+		_KVM_SET_SIGNAL_MASK,
+		uintptr(unsafe.Pointer(&data))); errno != 0 {
+		return fmt.Errorf("error setting signal mask: %v", errno)
+	}
+
+	return nil
+}
+
 // SwitchToUser unpacks architectural-details.
 func (c *vCPU) SwitchToUser(switchOpts ring0.SwitchOpts, info *arch.SignalInfo) (usermem.AccessType, error) {
 	// Check for canonical addresses.
diff --git a/pkg/sentry/platform/kvm/machine_unsafe.go b/pkg/sentry/platform/kvm/machine_unsafe.go
index e4de0a889..f04be2ab5 100644
--- a/pkg/sentry/platform/kvm/machine_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_unsafe.go
@@ -87,47 +87,6 @@ func unmapRunData(r *runData) error {
 	return nil
 }
 
-// setSignalMask sets the vCPU signal mask.
-//
-// This will be called from the bluepill handler, and therefore must not
-// perform any allocation.
-//
-//go:nosplit
-func (c *vCPU) setSignalMask(enableOthers bool) {
-	// The signal mask is either:
-	// *) Only the bounce signal, which we need to use to execute the
-	//    machine state up until the bounce interrupt can be processed.
-	//    or
-	// *) All signals, which is the default state unless we need to
-	//    continue execution to exit guest mode (the case above).
-	mask := bounceSignalMask
-	if enableOthers {
-		mask |= otherSignalsMask
-	}
-	if c.signalMask == mask {
-		return // Already set.
-	}
-
-	// The layout of this structure implies that it will not necessarily be
-	// the same layout chosen by the Go compiler. It gets fudged here.
-	var data struct {
-		length uint32
-		mask1  uint32
-		mask2  uint32
-		_      uint32
-	}
-	data.length = 8 // Fixed sigset size.
-	data.mask1 = ^uint32(mask & 0xffffffff)
-	data.mask2 = ^uint32(mask >> 32)
-	if _, _, errno := syscall.RawSyscall(
-		syscall.SYS_IOCTL,
-		uintptr(c.fd),
-		_KVM_SET_SIGNAL_MASK,
-		uintptr(unsafe.Pointer(&data))); errno != 0 {
-		throw("setSignal mask failed")
-	}
-}
-
 // atomicAddressSpace is an atomic address space pointer.
 type atomicAddressSpace struct {
 	pointer unsafe.Pointer
diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index 6c15727fa..8de75ae57 100644
--- a/runsc/sandbox/sandbox.go
+++ b/runsc/sandbox/sandbox.go
@@ -444,6 +444,12 @@ func (s *Sandbox) createSandboxProcess(conf *boot.Config, args *Args, startSyncF
 		nextFD++
 	}
 
+	// TODO(b/151157106): syscall tests fail by timeout if asyncpreemptoff
+	// isn't set.
+	if conf.Platform == "kvm" {
+		cmd.Env = append(cmd.Env, "GODEBUG=asyncpreemptoff=1")
+	}
+
 	// The current process' stdio must be passed to the application via the
 	// --stdio-fds flag. The stdio of the sandbox process itself must not
 	// be connected to the same FDs, otherwise we risk leaking sandbox