Re: [PATCH v3 10/10] arm64: Change type of hsr, cpsr, spsr_el1 to uint64_t

[Julien Grall <julien@xxxxxxx>]

Hi,

On 11/05/2021 07:37, Michal Orzel wrote:
> On 05.05.2021 10:00, Jan Beulich wrote:
> > On 05.05.2021 09:43, Michal Orzel wrote:
> > > --- a/xen/include/public/arch-arm.h
> > > +++ b/xen/include/public/arch-arm.h
> > > @@ -267,10 +267,10 @@ struct vcpu_guest_core_regs
> > >   
> > >       /* Return address and mode */
> > >       __DECL_REG(pc64,         pc32);             /* ELR_EL2 */
> > > -    uint32_t cpsr;                              /* SPSR_EL2 */
> > > +    uint64_t cpsr;                              /* SPSR_EL2 */
> > >   
> > >       union {
> > > -        uint32_t spsr_el1;       /* AArch64 */
> > > +        uint64_t spsr_el1;       /* AArch64 */
> > >           uint32_t spsr_svc;       /* AArch32 */
> > >       };
> > This change affects, besides domctl, also default_initialise_vcpu(),
> > which Arm's arch_initialise_vcpu() calls. I realize do_arm_vcpu_op()
> > only allows two unrelated VCPUOP_* to pass, but then I don't
> > understand why arch_initialise_vcpu() doesn't simply return e.g.
> > -EOPNOTSUPP. Hence I suspect I'm missing something.
I think it is just an overlooked when reviewing the following commit:

commit 192df6f9122ddebc21d0a632c10da3453aeee1c2
Author: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Date:   Tue Dec 15 14:12:32 2015 +0100

    x86: allow HVM guests to use hypercalls to bring up vCPUs

    Allow the usage of the VCPUOP_initialise, VCPUOP_up, VCPUOP_down,
    VCPUOP_is_up, VCPUOP_get_physid and VCPUOP_send_nmi hypercalls from HVM
    guests.

    This patch introduces a new structure (vcpu_hvm_context) that 
should be used
    in conjuction with the VCPUOP_initialise hypercall in order to 
initialize
    vCPUs for HVM guests.

    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

On Arm, the structure vcpu_guest_context is not exposed outside of Xen 
and the tools. Interestingly vcpu_guest_core_regs is but it should only 
be used within vcpu_guest_context.
So as this is not used by stable ABI, it is fine to break it.

> >
> I agree that do_arm_vcpu_op only allows two VCPUOP* to pass and
> arch_initialise_vcpu being called in case of VCPUOP_initialise
> has no sense as VCPUOP_initialise is not supported on arm.
> It makes sense that it should return -EOPNOTSUPP.
> However do_arm_vcpu_op will not accept VCPUOP_initialise and will return
> -EINVAL. So arch_initialise_vcpu for arm will not be called.
> Do you think that changing this behaviour so that arch_initialise_vcpu returns
> -EOPNOTSUPP should be part of this patch?
I think this change is unrelated. So it should be handled in a follow-up 
patch.
If you are taking care of this, would you mind to also look to move 
struct vcpu_guest_core_regs within the #if defined(__XEN__) || 
defined(__XEN_TOOLS__)?
I will attempt to do a proper review of this patch by the end of the week.

Cheers,

--
Julien Grall