Re: Questions about the qemu DCD support in cxl-2023-09-13

[fan <nifan.cxl@gmail.com>]

On Mon, Oct 23, 2023 at 12:48:02PM -0700, fan wrote:
> On Thu, Sep 21, 2023 at 03:24:26PM -0700, Ira Weiny wrote:
> > Fan,
> > 
> > I'm working off of Jonathan's latest CXL branch with the DCD patches.[1]
> > 
> > I've been testing various things and so far I have a couple of questions.
> > 
> > 1) If the qmp command is used to add extents which overlap other extents
> >    shouldn't that throw an error?  I don't see any validation of this and
> >    I would think a real device would reject such a request from the FM.
> > 
> > 2) Where is CXLType3Dev->dc.total_extent_count set?  Attempting to add
> >    extents prior to driver load does not seem to work.  And I think this
> >    is because total_extent_count is 0 in cmd_dcd_get_dyn_cap_ext_list().
> > 
> > Ira
> > 
> > [1] https://gitlab.com/jic23/qemu/-/tree/cxl-2023-09-13
> 
> Hi Ira,
> FYI. I have updated the DCD emulation patch series based on feedbacks on
> the previous version.
> 
> The new version is here:
> https://github.com/moking/qemu-jic-clone/tree/dcd-dev
> 
> The code is based on Jonathan's branch cxl-2023-09-26.
> 
> The main changes include,
> 
> 1. Update cxl_find_dc_region to detect the case the range of
> the extent cross multiple DC regions.
> 2. Add comments to explain the checks performed in function
> cxl_detect_malformed_extent_list. (Jonathan)
> 3. Minimize the checks in cmd_dcd_add_dyn_cap_rsp.(Jonathan)
> 4. Update total_extent_count in add/release dynamic capacity response function.
> (Ira and Jorgen Hansen).
> 5. Fix the logic issue in test_bits and renamed it to
> test_any_bits_set to clear its function.
> 6. Add pending extent list for add/release extent event.
> 7. When add/release extent response is received, use the pending list to
> verify the extents are valid.
> 8. Add test_any_bits_set and cxl_insert_extent_to_extent_list declaration to
> cxl_device.h so it can be used in different files.
> 9. Updated ct3d_qmp_cxl_event_log_enc to include dynamic capacity event log type.
> 10. Extract the functionality to delete extent from extent list to a helper
> function.
> 11. Move the update of the bitmap which reflects which blocks are backed with
> dc extents from the moment when a dc extent is offered to the moment when it
> is accepted from the host.
> 
> I was able to test the DCD code you sent previously, let me know if you
> find any issues.
> 
> Fan

FYI. 

Updated the last two commits to drop the extents for pending to
release as the host can proactively release dc extents so there can be
no pending-to-release extent list on the device side.

Fan