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

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 4/16/26 9:50 AM, Jan Beulich wrote:
> On 10.04.2026 19:41, Andrew Cooper wrote:
> > On 10/04/2026 4:45 pm, Oleksii Kurochko wrote:
> > > diff --git a/xen/arch/riscv/time.c b/xen/arch/riscv/time.c
> > > index 7efa76fdbcb1..80f0e9ddae6a 100644
> > > --- a/xen/arch/riscv/time.c
> > > +++ b/xen/arch/riscv/time.c
> > > @@ -91,4 +90,23 @@ void __init preinit_xen_time(void)
> > >           panic("%s: ACPI isn't supported\n", __func__);
> > >   
> > >       boot_clock_cycles = get_cycles();
> > > +
> > > +    /* set_xen_timer must have been set by sbi_init() already */
> > > +    ASSERT(set_xen_timer);
> > > +
> > > +    if ( riscv_isa_extension_available(NULL, RISCV_ISA_EXT_sstc) )
> > > +    {
> > > +        set_xen_timer = sstc_set_xen_timer;
> > > +
> > > +        /*
> > > +         * A VS-timer interrupt becomes pending whenever the value of
> > > +         * (time + htimedelta) is greater than or equal to vstimecmp CSR.
> > > +         * Thereby to avoid spurious VS-timer irqs set vstimecmp CSR to
> > > +         * ULONG_MAX.
> > > +         */
> > > +        csr_write(CSR_VSTIMECMP, ULONG_MAX);
> > > +#ifdef CONFIG_RISCV_32
> > > +        csr_write(CSR_VSTIMECMPH, ULONG_MAX);
> > > +#endif
> > You've got this pattern twice in this patch alone, and these aren't the
> > only CSRs which are formed of pairs to get a 64bit value in 32bit mode.
> >
> > Sadly, the numbering isn't consistent for the high constant, but we can
> > let the compiler do most of the hard work for us.
> >
> > #ifdef CONFIG_RISCV_32
> > # define __csr_write32h(csr, val) csr_write(csr ## H, (val) >> 32)
> > #else
> > # define __csr_write32h(csr, val) (void)(csr, val)
> Just to mention: Since the comma is an operator here (not a lexical element
> separating function arguments), more parenthesization may be needed for
> Misra's sake.
I will define it in the next way:

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

Thanks


~ Oleksii