arm64 kvm: added the implementation of setSystemTimeLegacy()

I have added support for setSystemTimeLegacy() by setting cntvoff.

With this pr, TestRdtsc and other kvm syscall test cases(nanosleep,
wait...) can be passed on Arm64.

TO-DO: Add precise synchronization to KVM for Arm64.
Reference PR: https://github.com/google/gvisor/pull/4397

Signed-off-by: Bin Lu <bin.lu@arm.com>

4 files changed, 59 insertions, 32 deletions

diff --git a/pkg/sentry/platform/kvm/kvm_const_arm64.go b/pkg/sentry/platform/kvm/kvm_const_arm64.go
index 84df0f878..5831b9345 100644
--- a/pkg/sentry/platform/kvm/kvm_const_arm64.go
+++ b/pkg/sentry/platform/kvm/kvm_const_arm64.go
@@ -38,6 +38,8 @@ const (
 	_KVM_ARM64_REGS_SCTLR_EL1  = 0x603000000013c080
 	_KVM_ARM64_REGS_CPACR_EL1  = 0x603000000013c082
 	_KVM_ARM64_REGS_VBAR_EL1   = 0x603000000013c600
+	_KVM_ARM64_REGS_TIMER_CNT  = 0x603000000013df1a
+	_KVM_ARM64_REGS_CNTFRQ_EL0 = 0x603000000013df00
 )
 
 // Arm64: Architectural Feature Access Control Register EL1.
diff --git a/pkg/sentry/platform/kvm/machine.go b/pkg/sentry/platform/kvm/machine.go
index 61ed24d01..f70d761fd 100644
--- a/pkg/sentry/platform/kvm/machine.go
+++ b/pkg/sentry/platform/kvm/machine.go
@@ -25,6 +25,7 @@ import (
 	"gvisor.dev/gvisor/pkg/procid"
 	"gvisor.dev/gvisor/pkg/sentry/platform/ring0"
 	"gvisor.dev/gvisor/pkg/sentry/platform/ring0/pagetables"
+	ktime "gvisor.dev/gvisor/pkg/sentry/time"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
@@ -625,3 +626,35 @@ func (c *vCPU) BounceToKernel() {
 func (c *vCPU) BounceToHost() {
 	c.bounce(true)
 }
+
+// setSystemTimeLegacy calibrates and sets an approximate system time.
+func (c *vCPU) setSystemTimeLegacy() error {
+	const minIterations = 10
+	minimum := uint64(0)
+	for iter := 0; ; iter++ {
+		// Try to set the TSC to an estimate of where it will be
+		// on the host during a "fast" system call iteration.
+		start := uint64(ktime.Rdtsc())
+		if err := c.setTSC(start + (minimum / 2)); err != nil {
+			return err
+		}
+		// See if this is our new minimum call time. Note that this
+		// serves two functions: one, we make sure that we are
+		// accurately predicting the offset we need to set. Second, we
+		// don't want to do the final set on a slow call, which could
+		// produce a really bad result.
+		end := uint64(ktime.Rdtsc())
+		if end < start {
+			continue // Totally bogus: unstable TSC?
+		}
+		current := end - start
+		if current < minimum || iter == 0 {
+			minimum = current // Set our new minimum.
+		}
+		// Is this past minIterations and within ~10% of minimum?
+		upperThreshold := (((minimum << 3) + minimum) >> 3)
+		if iter >= minIterations && current <= upperThreshold {
+			return nil
+		}
+	}
+}
diff --git a/pkg/sentry/platform/kvm/machine_amd64.go b/pkg/sentry/platform/kvm/machine_amd64.go
index c67127d95..a8b729e62 100644
--- a/pkg/sentry/platform/kvm/machine_amd64.go
+++ b/pkg/sentry/platform/kvm/machine_amd64.go
@@ -252,38 +252,6 @@ func (c *vCPU) setSystemTime() error {
 	}
 }
 
-// setSystemTimeLegacy calibrates and sets an approximate system time.
-func (c *vCPU) setSystemTimeLegacy() error {
-	const minIterations = 10
-	minimum := uint64(0)
-	for iter := 0; ; iter++ {
-		// Try to set the TSC to an estimate of where it will be
-		// on the host during a "fast" system call iteration.
-		start := uint64(ktime.Rdtsc())
-		if err := c.setTSC(start + (minimum / 2)); err != nil {
-			return err
-		}
-		// See if this is our new minimum call time. Note that this
-		// serves two functions: one, we make sure that we are
-		// accurately predicting the offset we need to set. Second, we
-		// don't want to do the final set on a slow call, which could
-		// produce a really bad result.
-		end := uint64(ktime.Rdtsc())
-		if end < start {
-			continue // Totally bogus: unstable TSC?
-		}
-		current := end - start
-		if current < minimum || iter == 0 {
-			minimum = current // Set our new minimum.
-		}
-		// Is this past minIterations and within ~10% of minimum?
-		upperThreshold := (((minimum << 3) + minimum) >> 3)
-		if iter >= minIterations && current <= upperThreshold {
-			return nil
-		}
-	}
-}
-
 // nonCanonical generates a canonical address return.
 //
 //go:nosplit
diff --git a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
index 84992c06d..1344ed3c9 100644
--- a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
@@ -159,9 +159,33 @@ func (c *vCPU) initArchState() error {
 	}
 
 	c.floatingPointState = arch.NewFloatingPointData()
+
+	return c.setSystemTime()
+}
+
+// setTSC sets the counter Virtual Offset.
+func (c *vCPU) setTSC(value uint64) error {
+	var (
+		reg  kvmOneReg
+		data uint64
+	)
+
+	reg.addr = uint64(reflect.ValueOf(&data).Pointer())
+	reg.id = _KVM_ARM64_REGS_TIMER_CNT
+	data = uint64(value)
+
+	if err := c.setOneRegister(&reg); err != nil {
+		return err
+	}
+
 	return nil
 }
 
+// setSystemTime sets the vCPU to the system time.
+func (c *vCPU) setSystemTime() error {
+	return c.setSystemTimeLegacy()
+}
+
 //go:nosplit
 func (c *vCPU) loadSegments(tid uint64) {
 	// TODO(gvisor.dev/issue/1238):  TLS is not supported.