Re: [PATCH v6 07/12] xen: enable Dom0 to use SVE feature

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.04.2023 16:00, Luca Fancellu wrote:
>> On 24 Apr 2023, at 12:34, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 24.04.2023 08:02, Luca Fancellu wrote:
>>> @@ -30,9 +37,11 @@ int sve_context_init(struct vcpu *v);
>>> void sve_context_free(struct vcpu *v);
>>> void sve_save_state(struct vcpu *v);
>>> void sve_restore_state(struct vcpu *v);
>>> +bool sve_domctl_vl_param(int val, unsigned int *out);
>>>
>>> #else /* !CONFIG_ARM64_SVE */
>>>
>>> +#define opt_dom0_sve     (0)
>>> #define is_sve_domain(d) (0)
>>>
>>> static inline register_t compute_max_zcr(void)
>>> @@ -59,6 +68,11 @@ static inline void sve_context_free(struct vcpu *v) {}
>>> static inline void sve_save_state(struct vcpu *v) {}
>>> static inline void sve_restore_state(struct vcpu *v) {}
>>>
>>> +static inline bool sve_domctl_vl_param(int val, unsigned int *out)
>>> +{
>>> +    return false;
>>> +}
>>
>> Once again I don't see the need for this stub: opt_dom0_sve is #define-d
>> to plain zero when !ARM64_SVE, so the only call site merely requires a
>> visible declaration, and DCE will take care of eliminating the actual call.
> 
> I’ve tried to do that, I’ve put the declaration outside the ifdef so that it 
> was always included
> and I removed the stub, but I got errors on compilation because of undefined 
> function.
> For that reason  I left that change out.

Interesting. I don't see where the reference would be coming from.

>>> --- a/xen/common/kernel.c
>>> +++ b/xen/common/kernel.c
>>> @@ -314,6 +314,31 @@ int parse_boolean(const char *name, const char *s, 
>>> const char *e)
>>>     return -1;
>>> }
>>>
>>> +int __init parse_signed_integer(const char *name, const char *s, const 
>>> char *e,
>>> +                                long long *val)
>>> +{
>>> +    size_t slen, nlen;
>>> +    const char *str;
>>> +    long long pval;
>>> +
>>> +    slen = e ? ({ ASSERT(e >= s); e - s; }) : strlen(s);
>>
>> As per this "e" may come in as NULL, meaning that ...
>>
>>> +    nlen = strlen(name);
>>> +
>>> +    /* Check that this is the name we're looking for and a value was 
>>> provided */
>>> +    if ( (slen <= nlen) || strncmp(s, name, nlen) || (s[nlen] != '=') )
>>> +        return -1;
>>> +
>>> +    pval = simple_strtoll(&s[nlen + 1], &str, 0);
>>> +
>>> +    /* Number not recognised */
>>> +    if ( str != e )
>>> +        return -2;
>>
>> ... this is always going to lead to failure in that case. (I guess I could
>> have spotted this earlier, sorry.)
>>
>> As a nit, I'd also appreciate if style here (parenthesization in particular)
>> could match that of parse_boolean(), which doesn't put parentheses around
>> the operands of comparison operators (a few lines up from here). With the
>> other function in mind, I'm then not going to pick on the seemingly
>> redundant (with the subsequent strncmp()) "slen <= nlen", which has an
>> equivalent there as well.
> 
> You are right, do you think this will be ok:

It'll do, I guess.

> --- a/xen/common/kernel.c
> +++ b/xen/common/kernel.c
> @@ -324,11 +324,14 @@ int __init parse_signed_integer(const char *name, const 
> char *s, const char *e,
>      slen = e ? ({ ASSERT(e >= s); e - s; }) : strlen(s);
>      nlen = strlen(name);
>  
> +    if ( !e )
> +        e = s + slen;
> +
>      /* Check that this is the name we're looking for and a value was 
> provided */
> -    if ( (slen <= nlen) || strncmp(s, name, nlen) || (s[nlen] != '=') )
> +    if ( slen <= nlen || strncmp(s, name, nlen) || s[nlen] != '=' )
>          return -1;
>  
> -    pval = simple_strtoll(&s[nlen + 1], &str, 0);
> +    pval = simple_strtoll(&s[nlen + 1], &str, 10);
>  
>      /* Number not recognised */
>      if ( str != e )
> 
> 
> Please note that I’ve also included your comment about the base, which I 
> forgot to add, apologies for that.
> 
> slen <= nlen doesn’t seems redundant to me, I have that because I’m accessing 
> s[nlen] and I would like
> the string s to be at least > nlen

Right, but doesn't strncmp() guarantee that already?

Jan