enable kvm to support arm64

   There are 4 jobs were finished in this package:
  	1, Virtual machine initialization.
	2, Bluepill implementation.
	3, Move ring0.Vectors() into the address with 11-bits alignment.
	4, Basic support for "SwitchToUser".
Signed-off-by: Bin Lu <bin.lu@arm.com>
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/gvisor/pull/919 from lubinszARM:pr_kvm eedea52db451bf62722759009a9f14c54a69c55f
PiperOrigin-RevId: 285501256

1 files changed, 22 insertions, 2 deletions

diff --git a/pkg/sentry/platform/kvm/bluepill.go b/pkg/sentry/platform/kvm/bluepill.go
index 043de51b3..30dbb74d6 100644
--- a/pkg/sentry/platform/kvm/bluepill.go
+++ b/pkg/sentry/platform/kvm/bluepill.go
@@ -20,6 +20,7 @@ import (
 	"syscall"
 
 	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/platform/ring0"
 	"gvisor.dev/gvisor/pkg/sentry/platform/safecopy"
 )
 
@@ -36,6 +37,18 @@ func sighandler()
 func dieTrampoline()
 
 var (
+	// bounceSignal is the signal used for bouncing KVM.
+	//
+	// We use SIGCHLD because it is not masked by the runtime, and
+	// it will be ignored properly by other parts of the kernel.
+	bounceSignal = syscall.SIGCHLD
+
+	// bounceSignalMask has only bounceSignal set.
+	bounceSignalMask = uint64(1 << (uint64(bounceSignal) - 1))
+
+	// bounce is the interrupt vector used to return to the kernel.
+	bounce = uint32(ring0.VirtualizationException)
+
 	// savedHandler is a pointer to the previous handler.
 	//
 	// This is called by bluepillHandler.
@@ -45,6 +58,13 @@ var (
 	dieTrampolineAddr uintptr
 )
 
+// redpill invokes a syscall with -1.
+//
+//go:nosplit
+func redpill() {
+	syscall.RawSyscall(^uintptr(0), 0, 0, 0)
+}
+
 // dieHandler is called by dieTrampoline.
 //
 //go:nosplit
@@ -73,8 +93,8 @@ func (c *vCPU) die(context *arch.SignalContext64, msg string) {
 
 func init() {
 	// Install the handler.
-	if err := safecopy.ReplaceSignalHandler(syscall.SIGSEGV, reflect.ValueOf(sighandler).Pointer(), &savedHandler); err != nil {
-		panic(fmt.Sprintf("Unable to set handler for signal %d: %v", syscall.SIGSEGV, err))
+	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))
 	}
 
 	// Extract the address for the trampoline.