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Re: [Xen-devel] [PATCH v3 2/4] x86: add domctl cmd to set/get CDP code/data CBM



>>> On 14.09.15 at 05:27, <he.chen@xxxxxxxxxxxxxxx> wrote:
> --- a/xen/arch/x86/psr.c
> +++ b/xen/arch/x86/psr.c
> @@ -288,14 +288,39 @@ int psr_get_cat_l3_info(unsigned int socket, uint32_t 
> *cbm_len,
>      return 0;
>  }
>  
> -int psr_get_l3_cbm(struct domain *d, unsigned int socket, uint64_t *cbm)
> +int psr_get_l3_cbm(struct domain *d, unsigned int socket,
> +                   uint64_t *cbm, enum cbm_type type)
>  {
>      struct psr_cat_socket_info *info = get_cat_socket_info(socket);
> +    bool_t cdp_enabled = test_bit(socket, cdp_socket_enable);
>  
>      if ( IS_ERR(info) )
>          return PTR_ERR(info);
>  
> -    *cbm = info->cos_to_cbm[d->arch.psr_cos_ids[socket]].u.cbm;
> +    if ( type == PSR_CBM_TYPE_L3 && cdp_enabled )
> +        return -EXDEV;
> +
> +    if ( (type == PSR_CBM_TYPE_L3_CODE || type == PSR_CBM_TYPE_L3_DATA)
> +        && !cdp_enabled )
> +        return -EXDEV;

These checks really ought to go into the subsequent switch(). But
then I wonder why asking for code or data would be wrong when
!cdp_enabled? You could simple return the same mask for all three
variants in that case.

> +    switch ( type )
> +    {
> +        case PSR_CBM_TYPE_L3:
> +            *cbm = info->cos_to_cbm[d->arch.psr_cos_ids[socket]].u.cbm;
> +            break;
> +
> +        case PSR_CBM_TYPE_L3_CODE:
> +            *cbm = info->cos_to_cbm[d->arch.psr_cos_ids[socket]].u.cdp.code;
> +            break;
> +
> +        case PSR_CBM_TYPE_L3_DATA:
> +            *cbm = info->cos_to_cbm[d->arch.psr_cos_ids[socket]].u.cdp.data;
> +            break;
> +
> +        default:
> +            return -EINVAL;

Considering that this is a helper function and "type" comes from a
caller inside the hypervisor, I'd really like to see an
ASSERT_UNREACHABLE() here.

> @@ -369,10 +394,53 @@ static int write_l3_cbm(unsigned int socket, unsigned 
> int cos,
>      return 0;
>  }
>  
> -int psr_set_l3_cbm(struct domain *d, unsigned int socket, uint64_t cbm)
> +static int find_cos(struct psr_cat_cbm *map, int cos_max,
> +                    uint64_t cbm_code, uint64_t cbm_data, bool_t cdp_enabled)
>  {
> -    unsigned int old_cos, cos;
> -    struct psr_cat_cbm *map, *found = NULL;
> +    unsigned int cos;
> +
> +    if ( !cdp_enabled )
> +    {
> +        for ( cos = 0; cos <= cos_max; cos++ )
> +            if ( map[cos].ref && map[cos].u.cbm == cbm_code )
> +                return cos;
> +    }
> +    else
> +    {
> +        for ( cos = 0; cos <= cos_max; cos++ )
> +            if ( map[cos].ref && map[cos].u.cdp.code == cbm_code &&
> +                 map[cos].u.cdp.data == cbm_data )
> +                return cos;
> +    }

I think having just a single loop here with a suitable conditional
expression inside the if() would both shrink code size and allow
the compiler to produce better (smaller) code.

> +static int pick_avail_cos(struct psr_cat_cbm *map, int cos_max, int old_cos)
> +{
> +    int cos;

In the function right above "cos" was unsigned int, which I think
is the correct type (also for "old_cos" and "cos_max").

> +int psr_set_l3_cbm(struct domain *d, unsigned int socket,
> +                   uint64_t cbm, enum cbm_type type)
> +{
> +    unsigned int old_cos, cos_max;
> +    int cos, ret;

Whereas here I can see why it should be plain int.

> @@ -381,53 +449,79 @@ int psr_set_l3_cbm(struct domain *d, unsigned int 
> socket, uint64_t cbm)
>      if ( !psr_check_cbm(info->cbm_len, cbm) )
>          return -EINVAL;
>  
> +    if ( !cdp_enabled && (type == PSR_CBM_TYPE_L3_CODE ||
> +        type == PSR_CBM_TYPE_L3_DATA) )
> +        return -EINVAL;
> +
> +    cos_max = info->cos_max;
>      old_cos = d->arch.psr_cos_ids[socket];
>      map = info->cos_to_cbm;
>  
> -    spin_lock(&info->cbm_lock);
>  
> -    for ( cos = 0; cos <= info->cos_max; cos++ )
> +    switch( type )
>      {
> -        /* If still not found, then keep unused one. */
> -        if ( !found && cos != 0 && map[cos].ref == 0 )
> -            found = map + cos;
> -        else if ( map[cos].u.cbm == cbm )
> -        {
> -            if ( unlikely(cos == old_cos) )
> -            {
> -                ASSERT(cos == 0 || map[cos].ref != 0);
> -                spin_unlock(&info->cbm_lock);
> -                return 0;
> -            }
> -            found = map + cos;
> +        case PSR_CBM_TYPE_L3:
> +            cbm_code = cbm;
> +            cbm_data = cbm;

Wrong indentation.

>              break;
> -        }
> -    }
>  
> -    /* If old cos is referred only by the domain, then use it. */
> -    if ( !found && map[old_cos].ref == 1 )
> -        found = map + old_cos;
> +        case PSR_CBM_TYPE_L3_CODE:
> +            cbm_code = cbm;
> +            cbm_data = map[old_cos].u.cdp.data;
> +            break;
>  
> -    if ( !found )
> -    {
> -        spin_unlock(&info->cbm_lock);
> -        return -EOVERFLOW;
> +        case PSR_CBM_TYPE_L3_DATA:
> +            cbm_code = map[old_cos].u.cdp.code;
> +            cbm_data = cbm;
> +            break;
> +
> +        default:
> +            return -EINVAL;
>      }
>  
> -    cos = found - map;
> -    if ( found->u.cbm != cbm )
> +    spin_lock(&info->cbm_lock);
> +    cos = find_cos(map, cos_max, cbm_code, cbm_data, cdp_enabled);
> +    if ( cos >= 0 )
>      {
> -        int ret = write_l3_cbm(socket, cos, cbm, 0, 0);
> -
> -        if ( ret )
> +        if ( unlikely(cos == old_cos) )

Are you sure about the unlikely() here?

>          {
>              spin_unlock(&info->cbm_lock);
> -            return ret;
> +            return 0;
> +        }
> +    }
> +    else
> +    {
> +        cos = pick_avail_cos(map, cos_max, old_cos);
> +        if ( cos < 0 )
> +        {
> +            spin_unlock(&info->cbm_lock);
> +            return cos;
> +        }
> +
> +        /* We try to avoid writing MSR */
> +        if ( cdp_enabled )
> +        {
> +            if ( map[cos].u.cdp.code == cbm_code &&
> +                 map[cos].u.cdp.data == cbm_data )
> +                need_write = 0;
> +        }
> +        else
> +            need_write = map[cos].u.cbm == cbm_code ? 0 : 1;

Please write such without conditional expression (a comparison on
the right side of an assignment is quite fine). Also the scope of
"need_write" would better be reduced to the minimal required one.

> --- a/xen/include/asm-x86/psr.h
> +++ b/xen/include/asm-x86/psr.h
> @@ -49,6 +49,12 @@ struct psr_cmt {
>      struct psr_cmt_l3 l3;
>  };
>  
> +enum cbm_type {
> +    PSR_CBM_TYPE_L3         = 1,
> +    PSR_CBM_TYPE_L3_CODE    = 2,
> +    PSR_CBM_TYPE_L3_DATA    = 3,

It doesn't look like you require these values to be 1, 2, and 3
respectively. Please omit explicit values in such cases.

Jan

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