Re: [PATCH v4 2/2] KVM: s390: use cookies for ioeventfd

[Gleb Natapov <gleb@redhat.com>]

On Sun, Jul 14, 2013 at 12:25:16PM +0300, Gleb Natapov wrote:
> On Thu, Jul 04, 2013 at 08:54:32AM +0200, Paolo Bonzini wrote:
> > Il 03/07/2013 18:33, Cornelia Huck ha scritto:
> > > On Wed, 03 Jul 2013 17:30:40 +0200
> > > Paolo Bonzini <pbonzini@redhat.com> wrote:
> > > 
> > >> Il 03/07/2013 16:30, Cornelia Huck ha scritto:
> > >>> +	/*
> > >>> +	 * Return cookie in gpr 2, but don't overwrite the register if the
> > >>> +	 * diagnose will be handled by userspace.
> > >>> +	 */
> > >>> +	if (ret != -EOPNOTSUPP)
> > >>> +		vcpu->run->s.regs.gprs[2] = ret;
> > >>
> > >> I think this should now be "if (ret >= 0)".
> > > 
> > > Hm, we don't want to kill gpr 2's old contents if userspace will do
> > > something, which means -EOPNOTSUPP.
> > 
> > In the end kvm_io_bus_write_cookie only returns -EOPNOTSUPP if there is
> > an error, so it works.  But if this were to change, the code would
> > break.  That's why I suggested testing "ret >= 0" rather than "ret !=
> > -EOPNOTSUPP".  But in the end it is the same.
> > 
> > >>
> > >>>  	/* kvm_io_bus_write returns -EOPNOTSUPP if it found no match. */
> > >>
> > >> The comment is now obsolete.
> > > 
> > > s/kvm_io_bus_write/kvm_io_bus_write_cookie/ ? Otherwise, this is still
> > > true.
> > 
> > True but somewhat misplaced, it is basically saying the same thing as
> > the "Return cookie in gpr 2" comment just above.
> > 
> > Anyhow, these are very small details.  I changed kvm_io_bus_write to
> > kvm_io_bus_write_cookie in the comment and applied the patches to kvm-queue.
> > 
> 1/2 broke x86. QEMU prints "Invalid read from memory region kvm-pic" and
> guest hangs. Looks like IO is forwarded to userspace instead of in kernel device
> for some reason. Un-applying for now.
> 
OK, stupid typo. Will amend the commit instead of dropping.


diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6cde6fa..a86735d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2942,7 +2942,7 @@ static int __kvm_io_bus_read(struct kvm_io_bus *bus, struct kvm_io_range *range,
 		return -EOPNOTSUPP;
 
 	while (idx < bus->dev_count &&
-		kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
+		kvm_io_bus_sort_cmp(range, &bus->range[idx]) == 0) {
 		if (!kvm_iodevice_read(bus->range[idx].dev, range->addr,
 				       range->len, val))
 			return idx;
--
			Gleb.