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

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi guys,

On 17.05.2021 18:03, Julien Grall wrote:
> 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,
> 
FWICS, all the discussion is about creating the next patch fixing the 
VCPUOP_initialise function.
Is there anything left to do in this patch or are you going to ack it?

Cheers,
Michal