gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/ring0/pagetables/pcids_aarch64.s (about)

     1  // Copyright 2020 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //go:build arm64
    16  // +build arm64
    17  
    18  #include "funcdata.h"
    19  #include "textflag.h"
    20  
    21  #define ID_AA64MMFR0_ASIDBITS_SHIFT 4
    22  #define ID_AA64MMFR0_ASIDBITS_16 2
    23  #define TCR_EL1_AS_BIT 36
    24  
    25  // GetASIDBits return the system ASID bits, 8 or 16 bits.
    26  //
    27  // func GetASIDBits() uint8
    28  TEXT ·GetASIDBits(SB),NOSPLIT|NOFRAME,$0-1
    29  	// First, check whether 16bits ASID is supported.
    30  	// ID_AA64MMFR0_EL1.ASIDBITS[7:4] == 0010.
    31  	WORD $0xd5380700    // MRS ID_AA64MMFR0_EL1, R0
    32  	UBFX $ID_AA64MMFR0_ASIDBITS_SHIFT, R0, $4, R0
    33  	CMPW $ID_AA64MMFR0_ASIDBITS_16, R0
    34  	BNE bits_8
    35  
    36  	// Second, check whether 16bits ASID is enabled.
    37  	// TCR_EL1.AS[36] == 1.
    38  	WORD $0xd5382040    // MRS TCR_EL1, R0
    39  	TBZ  $TCR_EL1_AS_BIT, R0, bits_8
    40  	MOVD $16, R0
    41  	B done
    42  bits_8:
    43  	MOVD $8, R0
    44  done:
    45  	MOVB R0, ret+0(FP)
    46  	RET