Re: [Xen-devel] [PATCH 5/7] x86/domain: Optimise the order of actions in arch_domain_create()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/03/18 16:54, Jan Beulich wrote:
>>>> On 09.03.18 at 14:18, <andrew.cooper3@xxxxxxxxxx> wrote:
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -430,20 +430,37 @@ int arch_domain_create(struct domain *d, unsigned int 
>> domcr_flags,
>>                         struct xen_arch_domainconfig *config)
>>  {
>>      bool paging_initialised = false;
>> +    uint32_t emflags;
>>      int rc;
>>  
>> -    if ( config == NULL && !is_idle_domain(d) )
>> -        return -EINVAL;
>> -
>> -    d->arch.s3_integrity = domcr_flags & XEN_DOMCTL_CDF_s3_integrity;
>> -
>>      INIT_LIST_HEAD(&d->arch.pdev_list);
>>  
>>      d->arch.relmem = RELMEM_not_started;
>>      INIT_PAGE_LIST_HEAD(&d->arch.relmem_list);
>>  
>> -    if ( d->domain_id && !is_idle_domain(d) &&
>> -         cpu_has_amd_erratum(&boot_cpu_data, AMD_ERRATUM_121) )
>> +    spin_lock_init(&d->arch.e820_lock);
>> +    spin_lock_init(&d->arch.vtsc_lock);
>> +
>> +    /* Minimal initialisation for the idle domain. */
>> +    if ( unlikely(is_idle_domain(d)) )
>> +    {
>> +        static const struct arch_csw idle_csw = {
>> +            .from = paravirt_ctxt_switch_from,
>> +            .to   = paravirt_ctxt_switch_to,
>> +            .tail = continue_idle_domain,
>> +        };
>> +
>> +        d->arch.ctxt_switch = &idle_csw;
>> +
>> +        d->arch.cpuid = ZERO_BLOCK_PTR; /* Catch stray misuses. */
>> +        d->arch.msr = ZERO_BLOCK_PTR;
>> +
>> +        return 0;
>> +    }
>> +    else if ( !config )
> May I suggest to avoid the "else" here?

I've gone with

...
        return 0;
    }

    if ( !config )
    {
        /* Only IDLE is allowed with no config. */
        ASSERT_UNREACHABLE();
        return -EINVAL;
    }
...

For runtime safety and debug sanity.

~Andrew

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