Re: [PATCH v3 37/39] xen/riscv: implement continue_new_vcpu()

[Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>]

> continue_new_vcpu() is the arch hook invoked the first time a freshly
> created vCPU is scheduled. Implement both cases it has to cover:
>  - for the idle vCPU, switch to its own stack and jump to idle_loop();
>  - for a guest vCPU, enter the guest through the new
>    return_to_new_vcpu() path in entry.S, which restores hstatus and
>    sepc, passes the hart id in a0 and, in a1, either the DTB address
>    (boot vCPU, as expected by the RISC-V boot protocol) or the opaque
>    value passed to SBI HSM hart_start() (secondary vCPUs), clears the
>    remaining GPRs, sets sstatus.SPP and sstatus.SPIE and executes sret.
> 
Nit: the guest vCPU sentence is hard to follow in one go. Maybe split it:

  - for a guest vCPU, enter the guest through the new
    return_to_new_vcpu() path in entry.S. It restores hstatus and
    sepc and passes the hart id in a0. a1 holds the DTB address for
    the boot vCPU (as expected by the RISC-V boot protocol), or the
    opaque value passed to SBI HSM hart_start() for secondary vCPUs.
    It then clears the remaining GPRs, sets sstatus.SPP and
    sstatus.SPIE, and executes sret.

> [ ... 94 lines skipped ... ]
> --- a/xen/arch/riscv/entry.S
> +++ b/xen/arch/riscv/entry.S
> @@ -147,3 +147,42 @@ FUNC(__context_switch)
>  
>          ret
>  END(__context_switch)
> +
> +/*
> + * Enter a vCPU for the first time. Must be called with interrupts disabled,
> + * see continue_new_vcpu().
> + */
> +FUNC(return_to_new_vcpu)
> +        REG_L   t0, CPU_USER_REGS_HSTATUS(sp)
> +        csrw    CSR_HSTATUS, t0
> +
At this point regs->hstatus only has SPV | SPVP (arch_vcpu_create()), so
VSXL is written as 0, which is a reserved encoding. That only gets fixed
by "xen/riscv: set the guest's XLEN explicitly in hstatus.VSXL", which
comes later in the series. Wouldn't it be better to move that one ahead
of this patch?

Reviewed-by: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>

-- 
Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>