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Tony Krowiak 0cc00c8d40 s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks 
This patch fixes a lockdep splat introduced by commit f21916ec48
("s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated").
The lockdep splat only occurs when starting a Secure Execution guest.
Crypto virtualization (vfio_ap) is not yet supported for SE guests;
however, in order to avoid this problem when support becomes available,
this fix is being provided.

The circular locking dependency was introduced when the setting of the
masks in the guest's APCB was executed while holding the matrix_dev->lock.
While the lock is definitely needed to protect the setting/unsetting of the
matrix_mdev->kvm pointer, it is not necessarily critical for setting the
masks; so, the matrix_dev->lock will be released while the masks are being
set or cleared.

Keep in mind, however, that another process that takes the matrix_dev->lock
can get control while the masks in the guest's APCB are being set or
cleared as a result of the driver being notified that the KVM pointer
has been set or unset. This could result in invalid access to the
matrix_mdev->kvm pointer by the intervening process. To avoid this
scenario, two new fields are being added to the ap_matrix_mdev struct:

struct ap_matrix_mdev {
	...
	bool kvm_busy;
	wait_queue_head_t wait_for_kvm;
   ...
};

The functions that handle notification that the KVM pointer value has
been set or cleared will set the kvm_busy flag to true until they are done
processing at which time they will set it to false and wake up the tasks on
the matrix_mdev->wait_for_kvm wait queue. Functions that require
access to matrix_mdev->kvm will sleep on the wait queue until they are
awakened at which time they can safely access the matrix_mdev->kvm
field.

Fixes: f21916ec48 ("s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated")
Cc: stable@vger.kernel.org
Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
2021-04-05 11:30:58 +02:00
arch s390/cio: remove duplicate struct ccw1 declaration 2021-04-05 11:30:57 +02:00
block block: Discard page cache of zone reset target range 2021-03-11 11:49:25 -07:00
certs certs: Replace K{U,G}IDT_INIT() with GLOBAL_ROOT_{U,G}ID 2021-01-21 16:16:10 +00:00
crypto crypto: mips/poly1305 - enable for all MIPS processors 2021-03-08 11:52:17 +01:00
Documentation s390/pci: expose UID uniqueness guarantee 2021-04-05 11:30:57 +02:00
drivers s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks 2021-04-05 11:30:58 +02:00
fs Miscellaneous ext4 bug fixes for v5.12. 2021-03-21 14:06:10 -07:00
include USB / Thunderbolt driver fixes for 5.12-rc4 2021-03-21 11:49:16 -07:00
init Merge branch 'akpm' (patches from Andrew) 2021-03-14 12:23:34 -07:00
ipc fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
kernel io_uring-5.12-2021-03-21 2021-03-21 12:25:54 -07:00
lib kasan: fix KASAN_STACK dependency for HW_TAGS 2021-03-13 11:27:31 -08:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm Merge branch 'akpm' (patches from Andrew) 2021-03-14 12:23:34 -07:00
net module: remove never implemented MODULE_SUPPORTED_DEVICE 2021-03-17 13:16:18 -07:00
samples Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
scripts kbuild: fix ld-version.sh to not be affected by locale 2021-03-13 11:12:13 +09:00
security Revert 95ebabde38 ("capabilities: Don't allow writing ambiguous v3 file capabilities") 2021-03-12 15:27:14 -06:00
sound sound fixes for 5.12-rc4 2021-03-19 09:53:32 -07:00
tools selftests: kvm: add set_boot_cpu_id test 2021-03-18 13:55:14 -04:00
usr Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
virt KVM: x86/mmu: Consider the hva in mmu_notifier retry 2021-02-22 13:16:53 -05:00
.clang-format cxl for 5.12 2021-02-24 09:38:36 -08:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore clang-lto series for v5.12-rc1 2021-02-23 09:28:51 -08:00
.mailmap treewide: Miguel has moved 2021-02-26 09:41:03 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS treewide: Miguel has moved 2021-02-26 09:41:03 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: move the staging subsystem to lists.linux.dev 2021-03-16 12:17:26 +01:00
Makefile Linux 5.12-rc4 2021-03-21 14:56:43 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.