Re: [PATCH v2] cxl/core: Return error when cxl_endpoint_gather_bandwidth() handles a non-PCI device

[Dan Williams]

Li Zhijian wrote:
> The function cxl_endpoint_gather_bandwidth() invokes
> pci_bus_read/write_XXX(), however, not all CXL devices are presently
> implemented via PCI. It is recognized that the cxl_test has realized a CXL
> device using a platform device.


> Calling pci_bus_read/write_XXX() in cxl_test will cause kernel panic:

I like that you include the failure info. I would also trim it to just
the salient information, like this:

 platform cxl_host_bridge.3: host supports CXL (restricted)
 Oops: general protection fault, probably for non-canonical address 0x3ef17856fcae4fbd: 0000 [#1] PREEMPT SMP PTI
 RIP: 0010:pci_bus_read_config_word+0x1c/0x60
 Call Trace:
  <TASK>
  ? __die_body.cold+0x19/0x27
  ? die_addr+0x38/0x60
  ? exc_general_protection+0x1f5/0x4b0
  ? asm_exc_general_protection+0x22/0x30
  ? pci_bus_read_config_word+0x1c/0x60
  pcie_capability_read_word+0x93/0xb0
  pcie_link_speed_mbps+0x18/0x50
  cxl_pci_get_bandwidth+0x18/0x60 [cxl_core]
  cxl_endpoint_gather_bandwidth.constprop.0+0xf4/0x230 [cxl_core]
  ? xas_store+0x54/0x660
  ? preempt_count_add+0x69/0xa0
  ? _raw_spin_lock+0x13/0x40
  ? __kmalloc_cache_noprof+0xe7/0x270
  cxl_region_shared_upstream_bandwidth_update+0x9c/0x790 [cxl_core]
  cxl_region_attach+0x520/0x7e0 [cxl_core]
  store_targetN+0xf2/0x120 [cxl_core]

> And Ying also reported a KASAN error with similar calltrace.
> 
> Reported-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Closes: https://lore.kernel.org/linux-cxl/87y12w9vp5.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

Minor, but this can also be trimmed:

Closes: http://lore.kernel.org/87y12w9vp5.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

> Fixes: a5ab0de0ebaa ("cxl: Calculate region bandwidth of targets with shared upstream link")
> 
> Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
> ---
> V2:
>   Check device type in original cxl_endpoint_gather_bandwidth() instead of mocking a new one. # Dan
>   Also noticed that the existing cxl_switch_gather_bandwidth() also have the same check.
> Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
> ---
>  drivers/cxl/core/cdat.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/cxl/core/cdat.c b/drivers/cxl/core/cdat.c
> index ef1621d40f05..1a510e692ac0 100644
> --- a/drivers/cxl/core/cdat.c
> +++ b/drivers/cxl/core/cdat.c
> @@ -641,6 +641,9 @@ static int cxl_endpoint_gather_bandwidth(struct cxl_region *cxlr,
>  	void *ptr;
>  	int rc;
>  
> +	if (!dev_is_pci(cxlds->dev))
> +		return -EINVAL;

This should be -ENODEV or -ENXIO. If this error code ever leaked out to
userspace the application would think it passed an "invalid argument" vs
encountering "no such device".

Feel free to add:
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>

...after fixing that up.