SENDUIPI

Send User Interprocessor Interrupt

stableVMJITAOTinstruction

Encodings

Operand encoding

Each mode is a value of the Op/En column above. It says which field of the encoded instruction carries each operand, in the order they are written, and whether the instruction reads it, writes it or both.

Measured cost

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 063, 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.

Exceptions

Sources

• This instruction in the Intel manual
• Latency and throughput per microarchitecture