linux-kernel - Re: [RFC PATCH 0/2] cxl: BG operations and device sanitation

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Date:   Thu, 4 Aug 2022 11:13:20 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Davidlohr Bueso <dave@...olabs.net>, linux-cxl@...r.kernel.org
Cc:     dan.j.williams@...el.com, bwidawsk@...nel.org,
        Jonathan.Cameron@...wei.com, ira.weiny@...el.com,
        alison.schofield@...el.com, vishal.l.verma@...el.com,
        a.manzanares@...sung.com, mcgrof@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] cxl: BG operations and device sanitation


On 8/3/2022 9:50 PM, Davidlohr Bueso wrote:
> Hello,
>
> The following is a followup to some of the discussions around CXL device security
> and sanitation[0, 1]. It is marked as RFC mostly to see if the background handling
> will satisfy all users, not just sanitize/overwrite. For example there has been ideas
> to avoid command hogging the device and/or interleaving scan media regions instead
> of all in one, etc. More details in each patch, but:
>
> Patch 1 adds the required background cmd handling bits. While this is currently
> only polling, it would be good to know if there are any fundamental blockers for
> supporting irqs (beyond just background ops) between PCIe and CXL. For example,
> are there any requirements/difficulties that is not the standard MSI/MSI-X PCI
> vector allocation + devm_request_irq()? I have not looked at this into details but
> it the topic has come up in the past as delicate', iirc.
>
> Patch 2 implements the sanitation commands (overwrite and secure erase).
>
> As for testing, while I used the mock device to test the secure erase command, I
> ended up hacking up a prototype[2] for qemu to support overwrite and bg commands.
> So while the some of the paths this series introduces have been exercised, there
> is of course a lot more to do.
>
> Applies against Dave's cxl-security branch[2] which deals with the pmem-only bits.

 From the operational sense everything looks good to me. As for the 
polling delay on overwrite, with pre-CXL pmem on Optane, we've 
discovered that overwrite can take a long time depending on the size. 
Sometimes MANY hours if the size is really large. We just opted to 
increment the polling interval as time went on [1] instead of based on size.

[1]: 
https://elixir.bootlin.com/linux/v5.19/source/drivers/nvdimm/security.c#L434


> Thanks,
> Davidlohr
>
> [0]: https://lore.kernel.org/all/20220708172455.gi37dh3od4w5lqrd@offworld/
> [1]: https://lore.kernel.org/all/165791918718.2491387.4203738301057301285.stgit@djiang5-desk3.ch.intel.com/
> [2]: https://github.com/davidlohr/qemu/commit/64a93a5b824b59d3b547f06f7fbb1269fb4790ce
> [3]: https://git.kernel.org/pub/scm/linux/kernel/git/djiang/linux.git/log/?h=cxl-security
>
> Davidlohr Bueso (2):
>    cxl/mbox: Add background operation handling machinery
>    cxl/mem: Support sanitation commands
>
>   Documentation/ABI/testing/sysfs-bus-cxl |  19 ++
>   drivers/cxl/core/core.h                 |   2 +-
>   drivers/cxl/core/mbox.c                 | 304 +++++++++++++++++++++++-
>   drivers/cxl/core/memdev.c               |  58 +++++
>   drivers/cxl/core/port.c                 |   9 +-
>   drivers/cxl/cxl.h                       |   8 +
>   drivers/cxl/cxlmem.h                    |  65 ++++-
>   drivers/cxl/pci.c                       |   3 +-
>   drivers/cxl/pmem.c                      |   5 +-
>   drivers/cxl/security.c                  |  13 +-
>   include/uapi/linux/cxl_mem.h            |   2 +
>   11 files changed, 461 insertions(+), 27 deletions(-)
>
> --
> 2.37.1
>