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cxl: Prevent adapter reset if an active context exists

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This patch prevents resetting the cxl adapter via sysfs in presence of
one or more active cxl_context on it. This protects against an
unrecoverable error caused by PSL owning a dirty cache line even after
reset and host tries to touch the same cache line. In case a force reset
of the card is required irrespective of any active contexts, the int
value -1 can be stored in the 'reset' sysfs attribute of the card.

The patch introduces a new atomic_t member named contexts_num inside
struct cxl that holds the number of active context attached to the card
, which is checked against '0' before proceeding with the reset. To
prevent against a race condition where a context is activated just after
reset check is performed, the contexts_num is atomically set to '-1'
after reset-check to indicate that no more contexts can be activated on
the card anymore.

Before activating a context we atomically test if contexts_num is
non-negative and if so, increment its value by one. In case the value of
contexts_num is negative then it indicates that the card is about to be
reset and context activation is error-ed out at that point.

Fixes: 62fa19d4b4 ("cxl: Add ability to reset the card")
Cc: [email protected] # v4.0+
Acked-by: Frederic Barrat <[email protected]>
Reviewed-by: Andrew Donnellan <[email protected]>
Signed-off-by: Vaibhav Jain <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
This commit is contained in:
Vaibhav Jain 2016-10-14 15:08:36 +05:30 • committed by Michael Ellerman
commit 70b565bbdb
9 changed files with 121 additions and 7 deletions
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7
Documentation/ABI/testing/sysfs-class-cxl
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@ -220,8 +220,11 @@ What: /sys/class/cxl/<card>/reset
Date: October 2014
Contact: [email protected]
Description: write only
Writing 1 will issue a PERST to card which may cause the card
to reload the FPGA depending on load_image_on_perst.
Writing 1 will issue a PERST to card provided there are no
contexts active on any one of the card AFUs. This may cause
the card to reload the FPGA depending on load_image_on_perst.
Writing -1 will do a force PERST irrespective of any active
contexts on the card AFUs.
Users: https://github.com/ibm-capi/libcxl
What: /sys/class/cxl/<card>/perst_reloads_same_image (not in a guest)