Re: [PATCH v4 21/28] cxl/extent: Process DCD events and realize region extents

[Ira Weiny <ira.weiny@intel.com>]

Jonathan Cameron wrote:
> On Wed, 9 Oct 2024 14:49:09 -0500
> Ira Weiny <ira.weiny@intel.com> wrote:
> 
> > Li, Ming4 wrote:
> > > On 10/8/2024 7:16 AM, ira.weiny@intel.com wrote:  
> > > > From: Navneet Singh <navneet.singh@intel.com>
> > > >  

[snip]

> > 
> > > > +static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,
> > > > +				struct xarray *extent_array, int cnt)
> > > > +{
> > > > +	struct cxl_mailbox *cxl_mbox = &mds->cxlds.cxl_mbox;
> > > > +	struct cxl_mbox_dc_response *p;
> > > > +	struct cxl_mbox_cmd mbox_cmd;
> > > > +	struct cxl_extent *extent;
> > > > +	unsigned long index;
> > > > +	u32 pl_index;
> > > > +	int rc;
> > > > +
> > > > +	size_t pl_size = struct_size(p, extent_list, cnt);
> > > > +	u32 max_extents = cnt;
> > > > +
> > > > +	/* May have to use more bit on response. */
> > > > +	if (pl_size > cxl_mbox->payload_size) {
> > > > +		max_extents = (cxl_mbox->payload_size - sizeof(*p)) /
> > > > +			      sizeof(struct updated_extent_list);
> > > > +		pl_size = struct_size(p, extent_list, max_extents);
> > > > +	}
> > > > +
> > > > +	struct cxl_mbox_dc_response *response __free(kfree) =
> > > > +						kzalloc(pl_size, GFP_KERNEL);
> > > > +	if (!response)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	pl_index = 0;
> > > > +	xa_for_each(extent_array, index, extent) {
> > > > +
> > > > +		response->extent_list[pl_index].dpa_start = extent->start_dpa;
> > > > +		response->extent_list[pl_index].length = extent->length;
> > > > +		pl_index++;
> > > > +		response->extent_list_size = cpu_to_le32(pl_index);
> > > > +
> > > > +		if (pl_index == max_extents) {
> > > > +			mbox_cmd = (struct cxl_mbox_cmd) {
> > > > +				.opcode = opcode,
> > > > +				.size_in = struct_size(response, extent_list,
> > > > +						       pl_index),
> > > > +				.payload_in = response,
> > > > +			};
> > > > +
> > > > +			response->flags = 0;
> > > > +			if (pl_index < cnt)
> > > > +				response->flags &= CXL_DCD_EVENT_MORE;  
> > > 
> > > It should be 'response->flags |= CXL_DCD_EVENT_MORE' here.  
> > 
> > Ah yea.  Good catch.
> > 
> > > 
> > > Another issue is if 'cnt' is N times bigger than 'max_extents'(e,g. cnt=20, max_extents=10). all responses will be sent in this xa_for_each(), and CXL_DCD_EVENT_MORE will be set in the last response but it should not be set in these cases.
> > >   
> > 
> > Ah yes.  cnt must be decremented.  As I looked at the patch just now the
> > 
> > 	if (cnt == 0 || pl_index)
> > 
> > ... seemed very wrong to me.  That change masked this bug.
> > 
> > This should fix it:
> > 
> > diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> > index d66beec687a0..99200274dea8 100644
> > --- a/drivers/cxl/core/mbox.c
> > +++ b/drivers/cxl/core/mbox.c
> > @@ -1119,10 +1119,11 @@ static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,
> >                         if (rc)
> >                                 return rc;
> >                         pl_index = 0;
> > +                       cnt -= pl_index;
> >                 }
> >         }
> >  
> > -       if (cnt == 0 || pl_index) {
> 
> I thought this cnt == 0 check was to deal with the no valid
> extents case where an empty reply is needed.

Yes but the bug found by Ming needs to be handled too.  I see Fan is also
questioning this code.

So...  for clarity among all of us here is the new function.  I'm not thrilled
with the use of a goto but I think it is ok here.

Ira

static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,      
                               struct xarray *extent_array, int cnt)           
{                                                                              
       struct cxl_mailbox *cxl_mbox = &mds->cxlds.cxl_mbox;                    
       struct cxl_mbox_dc_response *p;                                         
       struct cxl_mbox_cmd mbox_cmd;                                           
       struct cxl_extent *extent;                                              
       unsigned long index;                                                    
       u32 pl_index;                                                           
       int rc;                                                                 
                                                                               
       size_t pl_size = struct_size(p, extent_list, cnt);                      
       u32 max_extents = cnt;                                                  
                                                                               
       /* May have to use more bit on response. */                             
       if (pl_size > cxl_mbox->payload_size) {                                 
               max_extents = (cxl_mbox->payload_size - sizeof(*p)) /           
                             sizeof(struct updated_extent_list);               
               pl_size = struct_size(p, extent_list, max_extents);             
       }                                                                       
                                                                               
       struct cxl_mbox_dc_response *response __free(kfree) =                   
                                               kzalloc(pl_size, GFP_KERNEL);   
       if (!response)                                                          
               return -ENOMEM;                                                 
                                                                               
       pl_index = 0;                                                           
       if (cnt == 0)                                                           
               goto send_zero_accepted;                                        
                                                                               
       xa_for_each(extent_array, index, extent) {                              
               response->extent_list[pl_index].dpa_start = extent->start_dpa;  
               response->extent_list[pl_index].length = extent->length;        
               pl_index++;                                                     
               response->extent_list_size = cpu_to_le32(pl_index);             
                                                                               
               if (pl_index == max_extents) {                                  
                       mbox_cmd = (struct cxl_mbox_cmd) {                      
                               .opcode = opcode,                               
                               .size_in = struct_size(response, extent_list,   
                                                      pl_index),               
                               .payload_in = response,                         
                       };                                                      
                                                                               
                       response->flags = 0;                                    
                       if (pl_index < cnt)                                     
                               response->flags &= CXL_DCD_EVENT_MORE;          
                                                                               
                       rc = cxl_internal_send_cmd(cxl_mbox, &mbox_cmd);        
                       if (rc)                                                 
                               return rc;                                      
                       cnt -= pl_index;                                        
                       pl_index = 0;                                           
               }                                                               
       }                                                                       
                                                                               
       if (!pl_index)                                                          
               return 0;                                                       
                                                                               
send_zero_accepted:                                                            
       mbox_cmd = (struct cxl_mbox_cmd) {                                      
               .opcode = opcode,                                               
               .size_in = struct_size(response, extent_list,                   
                                      pl_index),                               
               .payload_in = response,                                         
       };                                                                      
                                                                               
       response->flags = 0;                                                    
       return cxl_internal_send_cmd(cxl_mbox, &mbox_cmd);                      
}