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

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 17/05/2021 08:01, Jan Beulich wrote:
> On 12.05.2021 19:59, Julien Grall wrote:
> > 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.
> My only difference in viewing this is that I'd say the adjustment
> would better be a prereq patch to this one, such that the one here
> ends up being more obviously correct.
The function is already not reachable so I felt it was unfair to require 
the clean-up for merging this code.
> Also, if the function is
> indeed not meant to be reachable, besides making it return
> -EOPNOTSUPP (or alike) it should probably also have
> ASSERT_UNREACHABLE() added.
+1 on the idea.

Cheers,

--
Julien Grall