Re: [PATCH v2 03/39] xen/riscv: set the guest's XLEN explicitly in hstatus.VSXL

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 9/2/26 5:17 PM, Oleksii Kurochko wrote:
> On 9/2/26 4:31 PM, Jan Beulich wrote:
> > On 02.09.2026 15:29, Oleksii Kurochko wrote:
> > > On 9/2/26 3:07 PM, Jan Beulich wrote:
> > > > On 02.09.2026 13:42, Oleksii Kurochko wrote:
> > > > > It will also affect then common code as vcpu_csr_init() could be then
> > > > > called before domain type is set:
> > > > >
> > > > > +++ b/xen/common/device-tree/dom0less-build.c
> > > > > @@ -812,17 +812,18 @@ static int __init construct_domU(struct
> > > > > kernel_info *kinfo,
> > > > >         else if ( rc == 0 && !strcmp(dom0less_enhanced, "no- 
> > > > > xenstore") )
> > > > >             kinfo->dom0less_feature = DOM0LESS_ENHANCED_NO_XS;
> > > > >
> > > > > -    if ( vcpu_create(d, 0) == NULL )
> > > > > -        return -ENOMEM;
> > > > > -
> > > > >         d->max_pages = ((paddr_t)mem * SZ_1K) >> PAGE_SHIFT;
> > > > >
> > > > >         rc = kernel_probe(kinfo, node);
> > > > >         if ( rc < 0 )
> > > > >             return rc;
> > > > >
> > > > > +    /* The domain type needs to be known before the first vCPU is
> > > > > created. */
> > > > >         set_domain_type(d, kinfo);
> > > > >
> > > > > +    if ( vcpu_create(d, 0) == NULL )
> > > > > +        return -ENOMEM;
> > > > I don't understand the need for this, likely because I don't see why
> > > > domain_vsxl() would need calling from underneath vcpu_create().
> > > The call trace will be the following:
> > >     vcpu_create() -> arch_vcpu_create() -> vcpu_csr_init() ->
> > > domain_vsxldomain_vsxl()
> > >
> > >       unsigned int vsxl = domain_vsxl(v->domain);
> > >
> > >       ...
> > >
> > >       vcpu_guest_cpu_user_regs(v)->hstatus =
> > >           HSTATUS_SPV | HSTATUS_SPVP | MASK_INSR(vsxl, HSTATUS_VSXL);
> > >
> > > Without moving vcpu_create(d, 0) after set_domain_type(), domain_vsxl()
> > > will return something wrong.
> > Question is - do you need to set ->hstatus this early?
> Good point. I think that there is no really such need. It could be set 
> (at least, VSXL) just before jumping to new vCPU where we know domain 
> type for sure.
I planned to set VSXL bits here: 
https://lore.kernel.org/xen-devel/cover.1787838835.git.oleksii.kurochko@xxxxxxxxx/T/#m4144ea90815b48f2d281a2267cd28f50bd4cd54c
But it seems that I can't do that there as considering that platform can 
do VSXLEN == HSXLEN == 64 but someone will try do run
vCPU in 32bit mode we can't just crash domain in continue_new_vcpu().

Then still to set it in arch_vcpu_create() will be better (or in the 
construct_domain() if we want to avoid to change dom0less common code). 
At this stage it is easier to reject to create such vCPU which violates 
platform implementation.
~ Oleksii