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From: Peter Xu <peterx@redhat.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	qemu-devel@nongnu.org, "Michael S . Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH RFC 5/9] KVM: Provide helper to get kvm dirty log
Date: Wed, 25 Mar 2020 14:15:43 -0400
Message-ID: <20200325181543.GA404034@xz-x1> (raw)
In-Reply-To: <20200325175220.GD2635@work-vm>

On Wed, Mar 25, 2020 at 05:52:20PM +0000, Dr. David Alan Gilbert wrote:
> * Peter Xu (peterx@redhat.com) wrote:
> > Provide a helper kvm_slot_get_dirty_log() to make the function
> > kvm_physical_sync_dirty_bitmap() clearer.  We can even cache the as_id
> > into KVMSlot when it is created, so that we don't even need to pass it
> > down every time.
> > 
> > Since at it, remove return value of kvm_physical_sync_dirty_bitmap()
> > because it should never fail.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  accel/kvm/kvm-all.c      | 39 +++++++++++++++++++--------------------
> >  include/sysemu/kvm_int.h |  2 ++
> >  2 files changed, 21 insertions(+), 20 deletions(-)
> > 
> > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> > index bb635c775f..608216fd53 100644
> > --- a/accel/kvm/kvm-all.c
> > +++ b/accel/kvm/kvm-all.c
> > @@ -553,6 +553,18 @@ static void kvm_slot_init_dirty_bitmap(KVMSlot *mem)
> >      mem->dirty_bmap = g_malloc0(bitmap_size);
> >  }
> >  
> > +/* Sync dirty bitmap from kernel to KVMSlot.dirty_bmap */
> > +static void kvm_slot_get_dirty_log(KVMState *s, KVMSlot *slot)
> > +{
> > +    struct kvm_dirty_log d = {};
> > +    int ret;
> > +
> > +    d.dirty_bitmap = slot->dirty_bmap;
> > +    d.slot = slot->slot | (slot->as_id << 16);
> > +    ret = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
> > +    assert(ret != -1);
> 
> As discussed on irc, that -1 check seems odd given your previous check
> but there seems to be some history as to why it was still there.  Hmm.
> 
> It also seems very trusting that it can never possibly fail!

Yeah I agree.  I've asked the question under patch 1.

Before we know the answer, I'll remove the assertion to print an error
if it triggers; check against -1 (-EPERM) explicitly does look odd...

Thanks,

-- 
Peter Xu



  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-05 14:17 [PATCH RFC 0/9] KVM: Dirty ring support (QEMU part) Peter Xu
2020-02-05 14:17 ` [PATCH RFC 1/9] KVM: Fixup kvm_log_clear_one_slot() ioctl return check Peter Xu
2020-03-25 16:34   ` Dr. David Alan Gilbert
2020-03-25 17:43   ` Peter Xu
2020-02-05 14:17 ` [PATCH RFC 2/9] linux-headers: Update Peter Xu
2020-02-05 14:17 ` [PATCH RFC 3/9] memory: Introduce log_sync_global() to memory listener Peter Xu
2020-03-25 16:52   ` Dr. David Alan Gilbert
2020-03-25 17:02     ` Peter Xu
2020-02-05 14:17 ` [PATCH RFC 4/9] KVM: Create the KVMSlot dirty bitmap on flag changes Peter Xu
2020-03-25 17:44   ` Dr. David Alan Gilbert
2020-02-05 14:17 ` [PATCH RFC 5/9] KVM: Provide helper to get kvm dirty log Peter Xu
2020-03-25 17:52   ` Dr. David Alan Gilbert
2020-03-25 18:15     ` Peter Xu [this message]
2020-02-05 14:17 ` [PATCH RFC 6/9] KVM: Provide helper to sync dirty bitmap from slot to ramblock Peter Xu
2020-03-25 18:47   ` Dr. David Alan Gilbert
2020-02-05 14:17 ` [PATCH RFC 7/9] KVM: Cache kvm slot dirty bitmap size Peter Xu
2020-03-25 18:49   ` Dr. David Alan Gilbert
2020-02-05 14:17 ` [PATCH RFC 8/9] KVM: Add dirty-ring-size property Peter Xu
2020-03-25 20:00   ` Dr. David Alan Gilbert
2020-03-25 20:42     ` Peter Xu
2020-03-26 13:41       ` Dr. David Alan Gilbert
2020-03-26 16:03         ` Peter Xu
2020-03-25 20:14   ` Dr. David Alan Gilbert
2020-03-25 20:48     ` Peter Xu
2020-02-05 14:17 ` [PATCH RFC 9/9] KVM: Dirty ring support Peter Xu
2020-03-25 20:41   ` Dr. David Alan Gilbert
2020-03-25 21:32     ` Peter Xu
2020-03-26 14:14       ` Dr. David Alan Gilbert
2020-03-26 16:10         ` Peter Xu
2020-02-05 14:51 ` [PATCH RFC 0/9] KVM: Dirty ring support (QEMU part) no-reply
2020-03-03 17:32 ` Peter Xu

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