Linux内核中维护进程无关寄存器失败

我修改了ARM的硬件(在gem5上)，增加了两个寄存器.我希望它们独立于进程，每个进程都有自己的相应值存储在这些寄存器中，就像ttbr0一样.

我想修改Linux内核(v5.15.36)来维护这两个寄存器.我做了以下更改，但有一个失败，这两个寄存器的值变为0，这是没有意义的.

首先，我在pt_regs中添加了对应于这两个寄存器的变量，

struct pt_regs {
    union {
        struct user_pt_regs user_regs;
        struct {
            u64 regs[31];
            u64 sp;
            u64 pc;
            u64 pstate;
        };
    };

    // other original code .......

    u64 isa_domain;     // <================ my register
    u64 inst_priv_base; // <================ my register
};

我还在arch/arm/kernel/asm-offsets.h处添加了相应的宏定义:

  DEFINE(S_ISA_DOMAIN,          offsetof(struct pt_regs, isa_domain));
  DEFINE(S_INST_PRIV_BASE,          offsetof(struct pt_regs, inst_priv_base));

我将在copying_thread(fork的子函数)中初始化这两个寄存器，

int copy_thread(unsigned long clone_flags, unsigned long stack_start,
        unsigned long stk_sz, struct task_struct *p, unsigned long tls)
{
    struct pt_regs *childregs = task_pt_regs(p);
    memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context));

    fpsimd_flush_task_state(p);

    ptrauth_thread_init_kernel(p);

    if (likely(!(p->flags & (PF_KTHREAD | PF_IO_WORKER)))) {
        *childregs = *current_pt_regs();
        childregs->regs[0] = 0;
        // <=============== init the register
        childregs->inst_priv_base = isa_grid_get_inst_base_pa(user_id);
        regs->isa_domain = 1;
        // other code .....
    }
}

最后，我在堆栈kernel_entry和kernel_exit中保存并恢复它们.

.macro  kernel_entry, el, regsize = 64
    // some original code
    stp x24, x25, [sp, #16 * 12]
    stp x26, x27, [sp, #16 * 13]
    stp x28, x29, [sp, #16 * 14]

    // ISA-Grid
    .if \el == 0
    mrs x20, S3_7_C7_C1_0
    str x20, [sp, #S_ISA_DOMAIN]
    mrs x20, S3_7_C7_C1_1
    str x20, [sp, #S_INST_PRIV_BASE]
    .endif
    // some original code
.endm

.macro  kernel_exit, el
    // some original code
    apply_ssbd 0, x0, x1
    .endif

    msr elr_el1, x21            // set up the return data
    msr spsr_el1, x22

    // ISA-Grid
    .if \el == 0
    ldr x20, [sp, #S_ISA_DOMAIN]
    msr S3_7_C7_C1_0, x20
    ldr x20, [sp, #S_INST_PRIV_BASE]
    msr S3_7_C7_C1_1, x20
    .endif

    ldp x0, x1, [sp, #16 * 0]
    ldp x2, x3, [sp, #16 * 1]
    ldp x4, x5, [sp, #16 * 2]
    ldp x6, x7, [sp, #16 * 3]
    ldp x8, x9, [sp, #16 * 4]
    // some original code
.endm

但似乎有些时候寄存器的值为0(我不会将这两个寄存器初始化为0)，是否有一些维护步骤我错过了？