Patch "KVM: PPC: Book3S HV: Drop prepare_done from struct kvm_resize_hpt" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KVM: PPC: Book3S HV: Drop prepare_done from struct kvm_resize_hpt

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-ppc-book3s-hv-drop-prepare_done-from-struct-kvm_resize_hpt.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 3073774e638ef18d222465fe92bfc8fccb90d288 Mon Sep 17 00:00:00 2001
From: Serhii Popovych <spopovyc@redhat.com>
Date: Mon, 4 Dec 2017 09:36:41 -0500
Subject: KVM: PPC: Book3S HV: Drop prepare_done from struct kvm_resize_hpt

From: Serhii Popovych <spopovyc@redhat.com>

commit 3073774e638ef18d222465fe92bfc8fccb90d288 upstream.

Currently the kvm_resize_hpt structure has two fields relevant to the
state of an ongoing resize: 'prepare_done', which indicates whether
the worker thread has completed or not, and 'error' which indicates
whether it was successful or not.

Since the success/failure isn't known until completion, this is
confusingly redundant.  This patch consolidates the information into
just the 'error' value: -EBUSY indicates the worked is still in
progress, other negative values indicate (completed) failure, 0
indicates successful completion.

As a bonus this reduces size of struct kvm_resize_hpt by
__alignof__(struct kvm_hpt_info) and saves few bytes of code.

While there correct comment in struct kvm_resize_hpt which references
a non-existent semaphore (leftover from an early draft).

Assert with WARN_ON() in case of HPT allocation thread work runs more
than once for resize request or resize_hpt_allocate() returns -EBUSY
that is treated specially.

Change comparison against zero to make checkpatch.pl happy.

Signed-off-by: Serhii Popovych <spopovyc@redhat.com>
[dwg: Changed BUG_ON()s to WARN_ON()s and altered commit message for
 clarity]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/kvm/book3s_64_mmu_hv.c |   44 ++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 17 deletions(-)

--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -65,11 +65,17 @@ struct kvm_resize_hpt {
 	u32 order;
 
 	/* These fields protected by kvm->lock */
+
+	/* Possible values and their usage:
+	 *  <0     an error occurred during allocation,
+	 *  -EBUSY allocation is in the progress,
+	 *  0      allocation made successfuly.
+	 */
 	int error;
-	bool prepare_done;
 
-	/* Private to the work thread, until prepare_done is true,
-	 * then protected by kvm->resize_hpt_sem */
+	/* Private to the work thread, until error != -EBUSY,
+	 * then protected by kvm->lock.
+	 */
 	struct kvm_hpt_info hpt;
 };
 
@@ -1444,15 +1450,23 @@ static void resize_hpt_prepare_work(stru
 	struct kvm *kvm = resize->kvm;
 	int err;
 
+	if (WARN_ON(resize->error != -EBUSY))
+		return;
+
 	resize_hpt_debug(resize, "resize_hpt_prepare_work(): order = %d\n",
 			 resize->order);
 
 	err = resize_hpt_allocate(resize);
 
+	/* We have strict assumption about -EBUSY
+	 * when preparing for HPT resize.
+	 */
+	if (WARN_ON(err == -EBUSY))
+		err = -EINPROGRESS;
+
 	mutex_lock(&kvm->lock);
 
 	resize->error = err;
-	resize->prepare_done = true;
 
 	mutex_unlock(&kvm->lock);
 }
@@ -1477,14 +1491,12 @@ long kvm_vm_ioctl_resize_hpt_prepare(str
 
 	if (resize) {
 		if (resize->order == shift) {
-			/* Suitable resize in progress */
-			if (resize->prepare_done) {
-				ret = resize->error;
-				if (ret != 0)
-					resize_hpt_release(kvm, resize);
-			} else {
+			/* Suitable resize in progress? */
+			ret = resize->error;
+			if (ret == -EBUSY)
 				ret = 100; /* estimated time in ms */
-			}
+			else if (ret)
+				resize_hpt_release(kvm, resize);
 
 			goto out;
 		}
@@ -1504,6 +1516,8 @@ long kvm_vm_ioctl_resize_hpt_prepare(str
 		ret = -ENOMEM;
 		goto out;
 	}
+
+	resize->error = -EBUSY;
 	resize->order = shift;
 	resize->kvm = kvm;
 	INIT_WORK(&resize->work, resize_hpt_prepare_work);
@@ -1558,16 +1572,12 @@ long kvm_vm_ioctl_resize_hpt_commit(stru
 	if (!resize || (resize->order != shift))
 		goto out;
 
-	ret = -EBUSY;
-	if (!resize->prepare_done)
-		goto out;
-
 	ret = resize->error;
-	if (ret != 0)
+	if (ret)
 		goto out;
 
 	ret = resize_hpt_rehash(resize);
-	if (ret != 0)
+	if (ret)
 		goto out;
 
 	resize_hpt_pivot(resize);


Patches currently in stable-queue which might be from spopovyc@redhat.com are

queue-4.14/kvm-ppc-book3s-hv-drop-prepare_done-from-struct-kvm_resize_hpt.patch
queue-4.14/kvm-ppc-book3s-hv-fix-use-after-free-in-case-of-multiple-resize-requests.patch