Don't sched_setaffinity in ptrace platform.

PiperOrigin-RevId: 330777900

pkg/sentry/platform/ptrace/BUILD

@@ -30,7 +30,6 @@ go_library(
         "//pkg/safecopy",
         "//pkg/seccomp",
         "//pkg/sentry/arch",
-        "//pkg/sentry/hostcpu",
         "//pkg/sentry/memmap",
         "//pkg/sentry/platform",
         "//pkg/sentry/platform/interrupt",

pkg/sentry/platform/ptrace/filters.go

@@ -24,10 +24,9 @@ import (
 // SyscallFilters returns syscalls made exclusively by the ptrace platform.
 func (*PTrace) SyscallFilters() seccomp.SyscallRules {
 	return seccomp.SyscallRules{
-		unix.SYS_GETCPU:            {},
-		unix.SYS_SCHED_SETAFFINITY: {},
-		syscall.SYS_PTRACE:         {},
-		syscall.SYS_TGKILL:         {},
-		syscall.SYS_WAIT4:          {},
+		unix.SYS_GETCPU:    {},
+		syscall.SYS_PTRACE: {},
+		syscall.SYS_TGKILL: {},
+		syscall.SYS_WAIT4:  {},
 	}
 }

pkg/sentry/platform/ptrace/subprocess.go

@@ -518,11 +518,6 @@ func (s *subprocess) switchToApp(c *context, ac arch.Context) bool {
 	}
 	defer c.interrupt.Disable()
 
-	// Ensure that the CPU set is bound appropriately; this makes the
-	// emulation below several times faster, presumably by avoiding
-	// interprocessor wakeups and by simplifying the schedule.
-	t.bind()
-
 	// Set registers.
 	if err := t.setRegs(regs); err != nil {
 		panic(fmt.Sprintf("ptrace set regs (%+v) failed: %v", regs, err))

pkg/sentry/platform/ptrace/subprocess_linux_unsafe.go

@@ -18,29 +18,12 @@
 package ptrace
 
 import (
-	"sync/atomic"
 	"syscall"
 	"unsafe"
 
-	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/sentry/hostcpu"
-	"gvisor.dev/gvisor/pkg/sync"
 )
 
-// maskPool contains reusable CPU masks for setting affinity. Unfortunately,
-// runtime.NumCPU doesn't actually record the number of CPUs on the system, it
-// just records the number of CPUs available in the scheduler affinity set at
-// startup. This may a) change over time and b) gives a number far lower than
-// the maximum indexable CPU. To prevent lots of allocation in the hot path, we
-// use a pool to store large masks that we can reuse during bind.
-var maskPool = sync.Pool{
-	New: func() interface{} {
-		const maxCPUs = 1024 // Not a hard limit; see below.
-		return make([]uintptr, maxCPUs/64)
-	},
-}
-
 // unmaskAllSignals unmasks all signals on the current thread.
 //
 //go:nosplit
@@ -49,47 +32,3 @@ func unmaskAllSignals() syscall.Errno {
 	_, _, errno := syscall.RawSyscall6(syscall.SYS_RT_SIGPROCMASK, linux.SIG_SETMASK, uintptr(unsafe.Pointer(&set)), 0, linux.SignalSetSize, 0, 0)
 	return errno
 }
-
-// setCPU sets the CPU affinity.
-func (t *thread) setCPU(cpu uint32) error {
-	mask := maskPool.Get().([]uintptr)
-	n := int(cpu / 64)
-	v := uintptr(1 << uintptr(cpu%64))
-	if n >= len(mask) {
-		// See maskPool note above. We've actually exceeded the number
-		// of available cores. Grow the mask and return it.
-		mask = make([]uintptr, n+1)
-	}
-	mask[n] |= v
-	if _, _, errno := syscall.RawSyscall(
-		unix.SYS_SCHED_SETAFFINITY,
-		uintptr(t.tid),
-		uintptr(len(mask)*8),
-		uintptr(unsafe.Pointer(&mask[0]))); errno != 0 {
-		return errno
-	}
-	mask[n] &^= v
-	maskPool.Put(mask)
-	return nil
-}
-
-// bind attempts to ensure that the thread is on the same CPU as the current
-// thread. This provides no guarantees as it is fundamentally a racy operation:
-// CPU sets may change and we may be rescheduled in the middle of this
-// operation. As a result, no failures are reported.
-//
-// Precondition: the current runtime thread should be locked.
-func (t *thread) bind() {
-	currentCPU := hostcpu.GetCPU()
-
-	if oldCPU := atomic.SwapUint32(&t.cpu, currentCPU); oldCPU != currentCPU {
-		// Set the affinity on the thread and save the CPU for next
-		// round; we don't expect CPUs to bounce around too frequently.
-		//
-		// (It's worth noting that we could move CPUs between this point
-		// and when the tracee finishes executing. But that would be
-		// roughly the status quo anyways -- we're just maximizing our
-		// chances of colocation, not guaranteeing it.)
-		t.setCPU(currentCPU)
-	}
-}