Merge pull request #5767 from avagin:mxcsr

PiperOrigin-RevId: 367730917

1 files changed, 19 insertions, 0 deletions

diff --git a/pkg/ring0/kernel_amd64.go b/pkg/ring0/kernel_amd64.go
index 92d2330cb..41dfd0bf9 100644
--- a/pkg/ring0/kernel_amd64.go
+++ b/pkg/ring0/kernel_amd64.go
@@ -250,6 +250,7 @@ func (c *CPU) SwitchToUser(switchOpts SwitchOpts) (vector Vector) {
 	}
 	SaveFloatingPoint(switchOpts.FloatingPointState.BytePointer()) // escapes: no. Copy out floating point.
 	WriteFS(uintptr(c.registers.Fs_base))                          // escapes: no. Restore kernel FS.
+	RestoreKernelFPState()                                         // escapes: no. Restore kernel MXCSR.
 	return
 }
 
@@ -321,3 +322,21 @@ func SetCPUIDFaulting(on bool) bool {
 func ReadCR2() uintptr {
 	return readCR2()
 }
+
+// kernelMXCSR is the value of the mxcsr register in the Sentry.
+//
+// The MXCSR control configuration is initialized once and never changed. Look
+// at src/cmd/compile/abi-internal.md in the golang sources for more details.
+var kernelMXCSR uint32
+
+// RestoreKernelFPState restores the Sentry floating point state.
+//
+//go:nosplit
+func RestoreKernelFPState() {
+	// Restore the MXCSR control configuration.
+	ldmxcsr(&kernelMXCSR)
+}
+
+func init() {
+	stmxcsr(&kernelMXCSR)
+}