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

Li, Ming4
2024-10-10T03:06:57Z

On 10/10/2024 3:49 AM, Ira Weiny 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;

should update cnt before pl_index is reset to 0.

the cnt is a one of parameters of cxl_send_dc_response(), that means the caller gives the value of cnt, is that possible if the size of extent_array is larger than cnt? Should skip remain extents in extent_array when cnt is equal to 0?

> }
> }
>
> - if (cnt == 0 || pl_index) {
> + if (pl_index) {
> mbox_cmd = (struct cxl_mbox_cmd) {
> .opcode = opcode,
> .size_in = struct_size(response, extent_list,
>
>
> Thank you, and sorry again for missing your feedback.
>
> Ira
>
> [snip]