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Subject[PATCH v2 1/2] KVM: PPC: Book3S HV: Drop prepare_done from struct kvm_resize_hpt and cleanups
Date
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>
---
arch/powerpc/kvm/book3s_64_mmu_hv.c | 44 +++++++++++++++++++++++--------------
1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 9660972..31fa710 100644
--- 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);
--
1.8.3.1
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