Re: [PATCH v4] xen/riscv: allow Xen to use SSTC while hiding it from guests

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.04.2026 09:24, Oleksii Kurochko wrote:
> --- a/xen/arch/riscv/include/asm/csr.h
> +++ b/xen/arch/riscv/include/asm/csr.h
> @@ -32,6 +32,20 @@
>                             : "memory" );                        \
>  })
>  
> +#ifdef CONFIG_RISCV_32
> +# define __csr_write32h(csr, val) csr_write(csr ## H, (val) >> 32)
> +#else
> +# define __csr_write32h(csr, val) ((void)(csr), (void)(val))

In order to be able to spot issues in 64-bit builds, how about

# define __csr_write32h(csr, val) ((void)csr ## H, (void)(val))

?

Apart from this, no matter that it was Andrew to suggest this, I'd like to
(once again) point out that identifiers starting with two underscores are
reserved. I don't see why a single underscore wouldn't do here. Or
alternatively csr__write32h().

> @@ -279,8 +299,6 @@ static int cf_check sbi_set_timer_v01(uint64_t 
> stime_value)
>      return sbi_err_map_xen_errno(ret.error);
>  }
>  
> -int (* __ro_after_init sbi_set_timer)(uint64_t stime_value) = 
> sbi_set_timer_v01;
> -
>  int sbi_remote_sfence_vma(const cpumask_t *cpu_mask, vaddr_t start,
>                            size_t size)
>  {
> @@ -360,10 +378,9 @@ int __init sbi_init(void)
>          }
>  
>          if ( sbi_probe_extension(SBI_EXT_TIME) > 0 )
> -        {
> -            sbi_set_timer = sbi_set_timer_v02;
> -            dprintk(XENLOG_INFO, "SBI v0.2 TIME extension detected\n");
> -        }
> +            set_xen_timer = sbi_set_timer_v02;
> +        else
> +            set_xen_timer = sbi_set_timer_v01;
>      }

Sadly this isn't quite equivalent to sbi_set_timer having had an initializer.
I would have wanted to suggest to use a constructor function, but we call
init_constructors() even later than do_initcalls() on both Arm and x86 (we
don't call the latter at all on RISC-V so far). Might it be necessary to
introduce sbi_early_init(), called very early during boot? Else how do you
guarantee no accidental use of the variable before it is first set?

Jan