SCXTNUM_EL3 | Jon's Arm Reference

Provides a number that can be used to separate out different context numbers with the EL3 exception level, for the purpose of protecting against side-channels using branch prediction and similar resources.

Configuration

This register is present only when EL3 is implemented, (FEAT_CSV2_2 is implemented or FEAT_CSV2_1p2 is implemented), and FEAT_AA64 is implemented. Otherwise, direct accesses to SCXTNUM_EL3 are UNDEFINED.

Attributes

Field descriptions

SCXTNUM, bits [63:0]:

Software Context Number. A number to identify the context within the EL3 exception level.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Access Instructions

Accesses to this register use the following encodings in the System register encoding space:

MRS <Xt>, SCXTNUM_EL3

(op0 = 0b11, op1 = 0b110, CRn = 0b1101, CRm = 0b0000, op2 = 0b111)

if !(HaveEL(EL3) && (IsFeatureImplemented(FEAT_CSV2_2) || IsFeatureImplemented(FEAT_CSV2_1p2)) && IsFeatureImplemented(FEAT_AA64)) then UNDEFINED; elsif PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then UNDEFINED; elsif PSTATE.EL == EL2 then UNDEFINED; elsif PSTATE.EL == EL3 then X[t, 64] = SCXTNUM_EL3;

MSR SCXTNUM_EL3, <Xt>

(op0 = 0b11, op1 = 0b110, CRn = 0b1101, CRm = 0b0000, op2 = 0b111)

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
SCXTNUM
SCXTNUM