kvm: share upper halves among all pagtables

Fixes: #509

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antfin.com>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/pkg/sentry/platform/kvm/machine.go b/pkg/sentry/platform/kvm/machine.go
index f70d761fd..e2fffc99b 100644
--- a/pkg/sentry/platform/kvm/machine.go
+++ b/pkg/sentry/platform/kvm/machine.go
@@ -41,6 +41,9 @@ type machine struct {
 	// slots are currently being updated, and the caller should retry.
 	nextSlot uint32
 
+	// upperSharedPageTables tracks the read-only shared upper of all the pagetables.
+	upperSharedPageTables *pagetables.PageTables
+
 	// kernel is the set of global structures.
 	kernel ring0.Kernel
 
@@ -199,9 +202,7 @@ func newMachine(vm int) (*machine, error) {
 	log.Debugf("The maximum number of vCPUs is %d.", m.maxVCPUs)
 	m.vCPUsByTID = make(map[uint64]*vCPU)
 	m.vCPUsByID = make([]*vCPU, m.maxVCPUs)
-	m.kernel.Init(ring0.KernelOpts{
-		PageTables: pagetables.New(newAllocator()),
-	}, m.maxVCPUs)
+	m.kernel.Init(m.maxVCPUs)
 
 	// Pull the maximum slots.
 	maxSlots, _, errno := syscall.RawSyscall(syscall.SYS_IOCTL, uintptr(m.fd), _KVM_CHECK_EXTENSION, _KVM_CAP_MAX_MEMSLOTS)
@@ -213,6 +214,13 @@ func newMachine(vm int) (*machine, error) {
 	log.Debugf("The maximum number of slots is %d.", m.maxSlots)
 	m.usedSlots = make([]uintptr, m.maxSlots)
 
+	// Create the upper shared pagetables and kernel(sentry) pagetables.
+	m.upperSharedPageTables = pagetables.New(newAllocator())
+	m.mapUpperHalf(m.upperSharedPageTables)
+	m.upperSharedPageTables.Allocator.(*allocator).base.Drain()
+	m.upperSharedPageTables.MarkReadOnlyShared()
+	m.kernel.PageTables = pagetables.NewWithUpper(newAllocator(), m.upperSharedPageTables, ring0.KernelStartAddress)
+
 	// Apply the physical mappings. Note that these mappings may point to
 	// guest physical addresses that are not actually available. These
 	// physical pages are mapped on demand, see kernel_unsafe.go.
@@ -226,7 +234,6 @@ func newMachine(vm int) (*machine, error) {
 
 		return true // Keep iterating.
 	})
-	m.mapUpperHalf(m.kernel.PageTables)
 
 	var physicalRegionsReadOnly []physicalRegion
 	var physicalRegionsAvailable []physicalRegion