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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// +build amd64
package kvm
import (
"fmt"
"sync/atomic"
"syscall"
"unsafe"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/time"
)
// loadSegments copies the current segments.
//
// This may be called from within the signal context and throws on error.
//
//go:nosplit
func (c *vCPU) loadSegments(tid uint64) {
if _, _, errno := syscall.RawSyscall(
syscall.SYS_ARCH_PRCTL,
linux.ARCH_GET_FS,
uintptr(unsafe.Pointer(&c.CPU.Registers().Fs_base)),
0); errno != 0 {
throw("getting FS segment")
}
if _, _, errno := syscall.RawSyscall(
syscall.SYS_ARCH_PRCTL,
linux.ARCH_GET_GS,
uintptr(unsafe.Pointer(&c.CPU.Registers().Gs_base)),
0); errno != 0 {
throw("getting GS segment")
}
atomic.StoreUint64(&c.tid, tid)
}
// setCPUID sets the CPUID to be used by the guest.
func (c *vCPU) setCPUID() error {
if _, _, errno := syscall.RawSyscall(
syscall.SYS_IOCTL,
uintptr(c.fd),
_KVM_SET_CPUID2,
uintptr(unsafe.Pointer(&cpuidSupported))); errno != 0 {
return fmt.Errorf("error setting CPUID: %v", errno)
}
return nil
}
// setSystemTime sets the TSC for the vCPU.
//
// This has to make the call many times in order to minimize the intrinsic
// error in the offset. Unfortunately KVM does not expose a relative offset via
// the API, so this is an approximation. We do this via an iterative algorithm.
// This has the advantage that it can generally deal with highly variable
// system call times and should converge on the correct offset.
func (c *vCPU) setSystemTime() error {
const (
_MSR_IA32_TSC = 0x00000010
calibrateTries = 10
)
registers := modelControlRegisters{
nmsrs: 1,
}
registers.entries[0] = modelControlRegister{
index: _MSR_IA32_TSC,
}
target := uint64(^uint32(0))
for done := 0; done < calibrateTries; {
start := uint64(time.Rdtsc())
registers.entries[0].data = start + target
if _, _, errno := syscall.RawSyscall(
syscall.SYS_IOCTL,
uintptr(c.fd),
_KVM_SET_MSRS,
uintptr(unsafe.Pointer(®isters))); errno != 0 {
return fmt.Errorf("error setting system time: %v", errno)
}
// 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. So we only count attempts
// within +/- 6.25% of our minimum as an attempt.
end := uint64(time.Rdtsc())
if end < start {
continue // Totally bogus.
}
half := (end - start) / 2
if half < target {
target = half
}
if (half - target) < target/8 {
done++
}
}
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
}
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