SENDUIPI — Send User Interprocessor Interrupt

Instruction Operand Encoding ¶

Description ¶

The SENDUIPI instruction sends the user interprocessor interrupt (IPI) indicated by its register operand. (The operand always has 64 bits; operand-size overrides such as the prefix 66 are ignored.)

SENDUIPI uses a data structure called the user-interrupt target table (UITT). This table is located at the linear address UITTADDR (in the IA32_UINTR_TT MSR); it comprises UITTSZ+1 16-byte entries, where UITTSZ = IA32_UINT_MISC[31:0]. SENDUIPI uses the UITT entry (UITTE) indexed by the instruction's register operand. Each UITTE has the following format:

• Bit 0: V, a valid bit.
• Bits 7:1 are reserved and must be 0.
• Bits 15:8: UV, the user-interrupt vector (in the range 0–63, so bits 15:14 must be 0).
• Bits 63:16 are reserved.
• Bits 127:64: UPIDADDR, the linear address of a user posted-interrupt descriptor (UPID). (UPIDADDR is 64-byte aligned, so bits 69:64 of each UITTE must be 0.)

Each UPID has the following format (fields and bits not referenced are reserved):

• Bit 0 (ON) indicates an outstanding notification. If this bit is set, there is a notification outstanding for one or more user interrupts in PIR.
• Bit 1 (SN) indicates that notifications should be suppressed. If this bit is set, agents (including SENDUIPI) should not send notifications when posting user interrupts in this descriptor.
• Bits 23:16 (NV) contain the notification vector. This is used by agents sending user-interrupt notifications (including SENDUIPI).
• Bits 63:32 (NDST) contain the notification destination. This is the target physical APIC ID (in xAPIC mode, bits 47:40 are the 8-bit APIC ID; in x2APIC mode, the entire field forms the 32-bit APIC ID).
• Bits 127:64 (PIF) contain posted-interrupt requests. There is one bit for each user-interrupt vector. There is a user-interrupt request for a vector if the corresponding bit is 1.

Although SENDUIPI may be executed at any privilege level, all of the instruction’s memory accesses (to a UITTE and a UPID) are performed with supervisor privilege.

SENDUIPI sends a user interrupt by posting a user interrupt with vector V in the UPID referenced by UPIDADDR and then sending, as an ordinary IPI, any notification interrupt specified in that UPID.

Operation ¶

IF reg > UITTSZ;
    THEN #GP(0);
FI;
read tempUITTE from 16 bytes at UITTADDR+ (reg « 4);
IF tempUITTE.V = 0 or tempUITTE sets any reserved bit
    THEN #GP(0);
FI;
read tempUPID from 16 bytes at tempUITTE.UPIDADDR;// under lock
IF tempUPID sets any reserved bits or bits that must be zero
    THEN #GP(0); // release lock
FI;
tempUPID.PIR[tempUITTE.UV] := 1;
IF tempUPID.SN = tempUPID.ON = 0
    THEN
        tempUPID.ON := 1;
        sendNotify := 1;
    ELSE sendNotify := 0;
FI;
write tempUPID to 16 bytes at tempUITTE.UPIDADDR;// release lock
IF sendNotify = 1
    THEN
        IF local APIC is in x2APIC mode
            THEN send ordinary IPI with vector tempUPID.NV
                to 32-bit physical APIC ID tempUPID.NDST;
            ELSE send ordinary IPI with vector tempUPID.NV
                to 8-bit physical APIC ID tempUPID.NDST[15:8];
        FI;
FI;

Flags Affected ¶

None.

Protected Mode Exceptions ¶

Real-Address Mode Exceptions ¶

Virtual-8086 Mode Exceptions ¶

Compatibility Mode Exceptions ¶

64-Bit Mode Exceptions ¶