Re: [Xen-devel] [PATCH v8 08/24] x86: refactor psr: set value: implement framework.

[Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx>]

On 17-02-26 17:41:43, Wei Liu wrote:
> On Wed, Feb 15, 2017 at 04:49:23PM +0800, Yi Sun wrote:
> [...]
> > +int psr_set_val(struct domain *d, unsigned int socket,
> > +                uint64_t val, enum cbm_type type)
> 
> IMHO it would be far better to use goto style error handling in such a
> complex function. You can avoid missing one of the exit paths when
> refactoring this function later.
> 
Ok, I will consider to use goto for error handling.

> > +{
> > +    unsigned int old_cos;
> > +    int cos, ret;
> > +    unsigned int *ref;
> > +    uint64_t *val_array;
> > +    struct psr_socket_info *info = get_socket_info(socket);
> > +    uint32_t array_len;
> > +    enum psr_feat_type feat_type;
> > +
> > +    if ( IS_ERR(info) )
> > +        return PTR_ERR(info);
> > +
> > +    feat_type = psr_cbm_type_to_feat_type(type);
> > +    if ( !test_bit(feat_type, &info->feat_mask) )
> > +        return -ENOENT;
> > +
> > +    /*
> > +     * Step 0:
> > +     * old_cos means the COS ID current domain is using. By default, it is 
> > 0.
> > +     *
> > +     * For every COS ID, there is a reference count to record how many 
> > domains
> > +     * are using the COS register corresponding to this COS ID.
> > +     * - If ref[old_cos] is 0, that means this COS is not used by any 
> > domain.
> > +     * - If ref[old_cos] is 1, that means this COS is only used by current
> > +     *   domain.
> > +     * - If ref[old_cos] is more than 1, that mean multiple domains are 
> > using
> > +     *   this COS.
> > +     */
> > +    old_cos = d->arch.psr_cos_ids[socket];
> > +    if ( old_cos > MAX_COS_REG_CNT )
> 
> How could this happen? This function is the setter of cos, it is a bug
> if it ever sets a value larger than MAX_COS_REG_CNT.
> 
You are right. This should not happen. This check is just a protection. If you
think it is not necessary, I will remove it.

> > +        return -EOVERFLOW;
> > +
> > +    ref = info->cos_ref;
> > +
> > +    /*
> > +     * Step 1:
> > +     * Assemle a value array to store all featues cos_reg_val[old_cos].
> > +     * And, set the input val into array according to the feature's
> > +     * position in array.
> > +     */
> > +    array_len = get_cos_num(info);
> > +    val_array = xzalloc_array(uint64_t, array_len);
> > +    if ( !val_array )
> > +        return -ENOMEM;
> > +
> > +    if ( (ret = assemble_val_array(val_array, array_len, info, old_cos)) 
> > != 0 )
> > +    {
> > +        xfree(val_array);
> > +        return ret;
> > +    }
> > +
> > +    if ( (ret = set_new_val_to_array(val_array, array_len, info,
> > +                                     feat_type, type, val)) != 0 )
> > +    {
> > +        xfree(val_array);
> > +        return ret;
> > +    }
> > +
> > +    /*
> > +     * Lock here to make sure the ref is not changed during find and
> > +     * write process.
> > +     */
> > +    spin_lock(&info->ref_lock);
> > +
> > +    /*
> > +     * Step 2:
> > +     * Try to find if there is already a COS ID on which all features' 
> > values
> > +     * are same as the array. Then, we can reuse this COS ID.
> > +     */
> > +    cos = find_cos(val_array, array_len, feat_type, info);
> > +    if ( cos >= 0 )
> > +    {
> > +        if ( cos == old_cos )
> > +        {
> > +            spin_unlock(&info->ref_lock);
> > +            xfree(val_array);
> > +            return 0;
> > +        }
> > +    }
> > +    else
> > +    {
> > +        /*
> > +         * Step 3:
> > +         * If fail to find, we need allocate a new COS ID.
> > +         * If multiple domains are using same COS ID, its ref is more
> > +         * than 1. That means we cannot free this COS to make current 
> > domain
> > +         * use it. Because other domains are using the value saved in the 
> > COS.
> > +         * Unless the ref is changed to 1 (mean only current domain is 
> > using
> > +         * it), we cannot allocate the COS ID to current domain.
> > +         * So, only the COS ID which ref is 1 or 0 can be allocated.
> > +         */
> > +        cos = pick_avail_cos(info, val_array, array_len, old_cos, 
> > feat_type);
> > +        if ( cos < 0 )
> > +        {
> > +            spin_unlock(&info->ref_lock);
> > +            xfree(val_array);
> > +            return cos;
> > +        }
> > +
> > +        /*
> > +         * Step 4:
> > +         * Write all features MSRs according to the COS ID.
> > +         */
> > +        ret = write_psr_msr(socket, cos, val_array);
> > +        if ( ret )
> > +        {
> > +            spin_unlock(&info->ref_lock);
> > +            xfree(val_array);
> > +            return ret;
> > +        }
> > +    }
> > +
> > +    /*
> > +     * Step 5:
> > +     * Update ref according to COS ID.
> > +     */
> > +    ref[cos]++;
> > +    ASSERT(ref[cos] || cos == 0);
> > +    ref[old_cos]--;
> > +    spin_unlock(&info->ref_lock);
> > +
> > +    /*
> > +     * Step 6:
> > +     * Save the COS ID into current domain's psr_cos_ids[] so that we can 
> > know
> > +     * which COS the domain is using on the socket. One domain can only use
> > +     * one COS ID at same time on each socket.
> > +     */
> > +    d->arch.psr_cos_ids[socket] = cos;
> > +    xfree(val_array);
> > +
> > +    return 0;
> > +}
> > +
> >  /* Called with domain lock held, no extra lock needed for 'psr_cos_ids' */
> >  static void psr_free_cos(struct domain *d)
> >  {
> > -    if( !d->arch.psr_cos_ids )
> > +    unsigned int socket, cos;
> > +
> > +    if ( !d->arch.psr_cos_ids )
> >          return;
> >  
> > +    /* Domain is free so its cos_ref should be decreased. */
> > +    for ( socket = 0; socket < nr_sockets; socket++ )
> > +    {
> > +        struct psr_socket_info *info;
> > +
> > +        /* cos 0 is default one which does not need be handled. */
> > +        if ( (cos = d->arch.psr_cos_ids[socket]) == 0 )
> 
> Break this into two lines. The assignment doesn't have to happen within
> if().
> 
Ok, thanks!

> Wei.

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