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

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.

Cc: stable@vger.kernel.org # v4.10+
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>

diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 9660972..f5f2c6b 100644 (file)
--- 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;
 };
 
@@ -1433,15 +1439,23 @@ static void resize_hpt_prepare_work(struct work_struct *work)
        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);
 }
@@ -1466,14 +1480,12 @@ long kvm_vm_ioctl_resize_hpt_prepare(struct kvm *kvm,
 
        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;
                }
@@ -1493,6 +1505,8 @@ long kvm_vm_ioctl_resize_hpt_prepare(struct kvm *kvm,
                ret = -ENOMEM;
                goto out;
        }
+
+       resize->error = -EBUSY;
        resize->order = shift;
        resize->kvm = kvm;
        INIT_WORK(&resize->work, resize_hpt_prepare_work);
@@ -1547,16 +1561,12 @@ long kvm_vm_ioctl_resize_hpt_commit(struct kvm *kvm,
        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);