um: add back support for FXSAVE registers

index 76eaeb93928c..eb1cdadc8a61 100644
@@ -18,6 +18,7 @@
 #include <registers.h>
 #include <sys/mman.h>
 
+static unsigned long ptrace_regset;
 unsigned long host_fp_size;
 
 int get_fp_registers(int pid, unsigned long *regs)

@@ -27,7 +28,7 @@ int get_fp_registers(int pid, unsigned long *regs)
 		.iov_len = host_fp_size,
 	};
 
-	if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
+	if (ptrace(PTRACE_GETREGSET, pid, ptrace_regset, &iov) < 0)
 		return -errno;
 	return 0;
 }

@@ -39,7 +40,7 @@ int put_fp_registers(int pid, unsigned long *regs)
 		.iov_len = host_fp_size,
 	};
 
-	if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
+	if (ptrace(PTRACE_SETREGSET, pid, ptrace_regset, &iov) < 0)
 		return -errno;
 	return 0;
 }

@@ -58,9 +59,23 @@ int arch_init_registers(int pid)
 		return -ENOMEM;
 
 	/* GDB has x86_xsave_length, which uses x86_cpuid_count */
-	ret = ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov);
+	ptrace_regset = NT_X86_XSTATE;
+	ret = ptrace(PTRACE_GETREGSET, pid, ptrace_regset, &iov);
 	if (ret)
 		ret = -errno;
+
+	if (ret == -ENODEV) {
+#ifdef CONFIG_X86_32
+		ptrace_regset = NT_PRXFPREG;
+#else
+		ptrace_regset = NT_PRFPREG;
+#endif
+		iov.iov_len = 2 * 1024 * 1024;
+		ret = ptrace(PTRACE_GETREGSET, pid, ptrace_regset, &iov);
+		if (ret)
+			ret = -errno;
+	}
+
 	munmap(iov.iov_base, 2 * 1024 * 1024);
 
 	host_fp_size = iov.iov_len;

index 75087e85b6fd..ea5b3bcc4245 100644
@@ -187,7 +187,12 @@ static int copy_sc_to_user(struct sigcontext __user *to,
 	 * Put magic/size values for userspace. We do not bother to verify them
 	 * later on, however, userspace needs them should it try to read the
 	 * XSTATE data. And ptrace does not fill in these parts.
+	 *
+	 * Skip this if we do not have an XSTATE frame.
 	 */
+	if (host_fp_size <= sizeof(to_fp64->fpstate))
+		return 0;
+
 	BUILD_BUG_ON(sizeof(int) != FP_XSTATE_MAGIC2_SIZE);
 #ifdef CONFIG_X86_32
 	__put_user(offsetof(struct _fpstate_32, _fxsr_env) +