WRPKRU—Write Data to User Page Key Register

Opcode*	Instruction	Op/En	64/32bit Mode Support	CPUID Feature Flag	Description
0F 01 EF	WRPKRU	NP	V/V	OSPKE	Writes EAX into PKRU.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
NP	NA	NA	NA	NA

Description

Writes the value of EAX into PKRU. ECX and EDX must be 0 when WRPKRU is executed; otherwise, a general-protection exception (#GP) occurs.

WRPKRU can be executed only if CR4.PKE = 1; otherwise, an invalid-opcode exception (#UD) occurs. Software can discover the value of CR4.PKE by examining CPUID.(EAX=07H,ECX=0H):ECX.OSPKE [bit 4].

On processors that support the Intel 64 Architecture, the high-order 32-bits of RCX, RDX and RAX are ignored.

Operation

IF (ECX = 0 AND EDX = 0)
    THEN PKRU ← EAX;
    ELSE #GP(0);
FI;

Flags Affected

None.

C/C++ Compiler Intrinsic Equivalent

WRPKRU:

void _wrpkru(uint32_t);

Protected Mode Exceptions

#GP(0)

If ECX ≠ 0.

If EDX ≠ 0.

#UD

If the LOCK prefix is used.

If CR4.PKE = 0.

Real-Address Mode Exceptions

Same exceptions as in protected mode.

Virtual-8086 Mode Exceptions

Same exceptions as in protected mode.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

Same exceptions as in protected mode.