Re: qemupatch问题请教

19 Oct 2021


      On 10/19/2021 2:26 PM, xuejinze wrote:
...
彭总您好，
很抱歉打扰您，有个qemu的问题想向您请教下。
关于commit *8e19c7e6*添加的kunpeng-920的cpu寄存器的定义，我对比了直接从
kunpeng920服务器上直接读出来的寄存器的值，有很多是和patch里面是有出入的。
想请教下修改中这些值是基于什么来定义的。
下面是我这台设备cpuinfo里面的信息：
processor : 95
model name : HUAWEI,Kunpeng 920
BogoMIPS : 200.00
Features : fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp
asimdhp cpuid asimdrdm jscvt fcma dcpop asimddp asimdfhm
CPU implementer : 0x48
CPU architecture: 8
CPU variant : 0x1
CPU part : 0xd01
CPU revision : 0
下面是我用的读取寄存器的程序：
/*
 * Sample program to demonstrate the MRS emulation ABI.
 *
 * Copyright (C) 2015-2016, ARM Ltd
 *
 * Author: Suzuki K Poulose <suzuki.poulose@arm.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */
#include <asm/hwcap.h>
#include <stdio.h>
#include <sys/auxv.h>
#define get_cpu_ftr(id) ({                                    \
              unsigned long __val;                            \
              asm("mrs %0, "#id : "=r" (__val));              \
              printf("%-20s: 0x%016lx\n", #id, __val);        \
      })
int main(void)
{
if (!(getauxval(AT_HWCAP) & HWCAP_CPUID)) {
              fputs("CPUID registers unavailable\n", stderr);
              return 1;
      }
get_cpu_ftr(ID_AA64ISAR0_EL1);
      get_cpu_ftr(ID_AA64ISAR1_EL1);
      get_cpu_ftr(ID_AA64MMFR0_EL1);
      get_cpu_ftr(ID_AA64MMFR1_EL1);
      get_cpu_ftr(ID_AA64PFR0_EL1);
      get_cpu_ftr(ID_AA64PFR1_EL1);
      get_cpu_ftr(ID_AA64DFR0_EL1);
      get_cpu_ftr(ID_AA64DFR1_EL1);
get_cpu_ftr(MIDR_EL1);
      get_cpu_ftr(MPIDR_EL1);
      get_cpu_ftr(REVIDR_EL1);
      get_cpu_ftr(CTR_EL0);
 #if 0
      /* Unexposed register access causes SIGILL */
      get_cpu_ftr(ID_MMFR0_EL1);
#endif
return 0;
}
下面是用以上程序读出来的值：
[root@host203 ~]# ./a.out
ID_AA64ISAR0_EL1 : 0x0001100010211120
ID_AA64ISAR1_EL1 : 0x0000000000011001
ID_AA64MMFR0_EL1 : 0x00000000ff000000
ID_AA64MMFR1_EL1 : 0x0000000000000000
ID_AA64PFR0_EL1 : 0x0000000000110011
ID_AA64PFR1_EL1 : 0x0000000000000000
ID_AA64DFR0_EL1 : 0x0000000000000006
ID_AA64DFR1_EL1 : 0x0000000000000000
MIDR_EL1 : 0x00000000481fd010
MPIDR_EL1 : 0x0000000080000000
REVIDR_EL1 : 0x0000000000000000
CTR_EL0 : 0x0000000084448004
我只对ID寄存器清除一点，其他的寄存器我也不是很清楚。所以下面说的都*只*针
对ID寄存器。

内核因为安全的原因，对于用户态的应用读取这些系统寄存器，只会呈现出一部分
值，还有一部分设置为了默认值，每个寄存器呈现出来的field的文档在
linux/Documentation/arm64/cpu-feature-registers.rst，就在这段代码的前面。

如果先要读取完整的寄存器值，可以写个内核模块在内核中读取。例如：
#include <linux/module.h>

#define get_idreg(id) printk("%-20s: 0x%016llx\n", #id,
read_sysreg_s(SYS_ ##id))

static int __init get_feature_init(void)
{
    get_idreg(ID_AA64ISAR0_EL1);
    get_idreg(ID_AA64ISAR1_EL1);
    get_idreg(ID_AA64MMFR0_EL1);
    get_idreg(ID_AA64MMFR1_EL1);
    get_idreg(ID_AA64PFR0_EL1);
    get_idreg(ID_AA64PFR1_EL1);
    get_idreg(ID_AA64DFR0_EL1);
    get_idreg(ID_AA64DFR1_EL1);

    get_idreg(MIDR_EL1);
    get_idreg(MPIDR_EL1);
    get_idreg(REVIDR_EL1);
    return 0;
}

static void __exit get_feature_exit(void)
{
}

module_init(get_feature_init);
module_exit(get_feature_exit);
MODULE_LICENSE("GPL");

在我的机器上插入内核模块后会在dmesg中打印如下信息：
[38928.608723] ID_AA64ISAR0_EL1    : 0x0001100010211120
[38928.608724] ID_AA64ISAR1_EL1    : 0x0000000000011001
[38928.608725] ID_AA64MMFR0_EL1    : 0x0000000000101125
[38928.608726] ID_AA64MMFR1_EL1    : 0x0000000010211122
[38928.608727] ID_AA64PFR0_EL1     : 0x0000010011111111
[38928.608727] ID_AA64PFR1_EL1     : 0x0000000000000000
[38928.608728] ID_AA64DFR0_EL1     : 0x0000000110305408
[38928.608729] ID_AA64DFR1_EL1     : 0x0000000000000000
[38928.608729] MIDR_EL1            : 0x00000000481fd010
[38928.608730] MPIDR_EL1           : 0x0000000081180300
[38928.608731] REVIDR_EL1          : 0x0000000000000000

具体隐藏的实现逻辑因为有段时间没有看这块代码了，有点记不太清了，所以下面
说的可能会有错误。在linux/arch/arm64/kernel/cpufeature.c中，定义了很多
ftr_id_*的变量，其中如果一个field定义为FTR_HIDDEN，则说明这个field对于用
户态是隐藏的。在init_cpu_ftr_reg中会根据定义的ftr_id_*初始化对应的
user_val、user_mask、sys_val。在用用户态读取这些寄存器的时候，在内核中会
调用到emulate_mrs，在这里面会根据之前初始化好的user_val、user_mask、
sys_val返回给用户态相应的值。


Thanks,
Peng

Peng Liang

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