cherry-pick: Protect read-only bits of syscfg #91
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
The Big QEMU Lock (BQL) has many names and they are confusing. The actual QemuMutex variable is called qemu_global_mutex but it's commonly referred to as the BQL in discussions and some code comments. The locking APIs, however, are called qemu_mutex_lock_iothread() and qemu_mutex_unlock_iothread(). The "iothread" name is historic and comes from when the main thread was split into into KVM vcpu threads and the "iothread" (now called the main loop thread). I have contributed to the confusion myself by introducing a separate --object iothread, a separate concept unrelated to the BQL. The "iothread" name is no longer appropriate for the BQL. Rename the locking APIs to: - void bql_lock(void) - void bql_unlock(void) - bool bql_locked(void) There are more APIs with "iothread" in their names. Subsequent patches will rename them. There are also comments and documentation that will be updated in later patches. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Paul Durrant <paul@xen.org> Acked-by: Fabiano Rosas <farosas@suse.de> Acked-by: David Woodhouse <dwmw@amazon.co.uk> Reviewed-by: Cédric Le Goater <clg@kaod.org> Acked-by: Peter Xu <peterx@redhat.com> Acked-by: Eric Farman <farman@linux.ibm.com> Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com> Acked-by: Hyman Huang <yong.huang@smartx.com> Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com> Message-id: 20240102153529.486531-2-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
The name "iothread" is overloaded. Use the term Big QEMU Lock (BQL) instead, it is already widely used and unambiguous. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Paul Durrant <paul@xen.org> Acked-by: David Woodhouse <dwmw@amazon.co.uk> Reviewed-by: Cédric Le Goater <clg@kaod.org> Acked-by: Ilya Leoshkevich <iii@linux.ibm.com> Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com> Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com> Message-id: 20240102153529.486531-3-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This lock is scope-bound - so we will avoid errors when adding new early
return statements.
BQL_LOCK_GUARD is an architecture-independent QEMU idiom to replace the
hexagon-specific {UN,}LOCK_IOTHREAD(). The hexagon-specific macro was
a pseudo-nested lock but we don't seem to need that flexibility if we
move the lock acquisition up to a consistent place high enough in the
call stack.
Signed-off-by: Brian Cain <bcain@quicinc.com>
Users may do a read-modify-write to update syscfg. Between the read of the original value of syscfg and the write of the new value another thread may do a k0lock/unlock or tlblock/unlock changing read-only bits k0 or tk. This patch protects those bits from being lost during the read-modify-write sequence. Signed-off-by: Sid Manning <sidneym@quicinc.com>
androm3da
approved these changes
Jul 15, 2024
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
No description provided.