On Thu, Feb 06, 2014 at 01:32:25PM +0100, Igor Mammedov wrote:
> On Thu, 6 Feb 2014 14:22:54 +0200
> "Michael S. Tsirkin" <m...@redhat.com> wrote:
>
> > On Thu, Feb 06, 2014 at 11:24:33AM +0100, Igor Mammedov wrote:
> > > Windows XP shows COM2 port as non functional in
> > > "Device Manager" although no COM2 port backing device
> > > is present in QEMU.
> > >
> > > That is caused by the fact that QEMU reports to
> > > OSPM that device is present by setting 5th bit in
> > > PII4XPM.pci_conf[0x67] register when COM2 doesn't
> > > exist.
> > >
> > > It happens due to memory_region_present(io_as, 0x2f8)
> > > returning false positive since 0x2f8 address eventually
> > > translates into catchall io_as address space.
> > >
> > > Fix memory_region_present(parent, addr) by returning
> > > true only if addr maps into a MemoryRegion within
> > > parent (excluding parent itself), to match its
> > > doc comment.
> > >
> > > While at it fix copy/paste error in
> > > memory_region_present() doc comment.
> > >
> > > Signed-off-by: Igor Mammedov <imamm...@redhat.com>
> >
> > Hmm, I wonder whether this still should return true
> > if parent is not a pure container.
> io_as in not a pure container, that's why
> memory_region_find() finds it at all.
Ah. So this regression is really due to
3bb28b7208b349e7a1b326e3c6ef9efac1d462bf?
I think we really need better handling for unassigned regions,
for memory we need it to implement master abort properly.
> This patch only fixes function to behave as it was
> originally documented.
>
> I guess we need to wait on Paolo's opinion, as an author
> if original code.
Well - consider what this function came to replace:
- pci_conf[0x67] = (memory_region_find(io_as, 0x3f8, 1).mr ? 0x08 : 0) |
- (memory_region_find(io_as, 0x2f8, 1).mr ? 0x90 : 0);
+ pci_conf[0x67] = (memory_region_present(io_as, 0x3f8) ? 0x08 : 0) |
+ (memory_region_present(io_as, 0x2f8) ? 0x90 : 0);
It's just that this function no longer works for io addresses.
> > Also what if MR isn't under parent at all?
> that function was never meant to handle this case.
>
> >
> > Maybe the right thing to do is
> > return mr->ops == &unassigned_mem_ops ?
> it could be but it looks more like a hack.
> i.e this exit conditions could pile up over time.
Sigh. It's all a hack, we need to handle errors better.
For now I'm ok with your patch.
> >
> >
> > > ---
> > > include/exec/memory.h | 6 +++---
> > > memory.c | 2 +-
> > > 2 files changed, 4 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/include/exec/memory.h b/include/exec/memory.h
> > > index 296d6ab..a5eb4c8 100644
> > > --- a/include/exec/memory.h
> > > +++ b/include/exec/memory.h
> > > @@ -838,13 +838,13 @@ void memory_region_set_alias_offset(MemoryRegion
> > > *mr,
> > > hwaddr offset);
> > >
> > > /**
> > > - * memory_region_present: translate an address/size relative to a
> > > - * MemoryRegion into a #MemoryRegionSection.
> > > + * memory_region_present: checks if an address relative to a @parent
> > > + * translates into #MemoryRegion within @parent
> > > *
> > > * Answer whether a #MemoryRegion within @parent covers the address
> > > * @addr.
> > > *
> > > - * @parent: a MemoryRegion within which @addr is a relative address
> > > + * @parent: a #MemoryRegion within which @addr is a relative address
> > > * @addr: the area within @parent to be searched
> > > */
> > > bool memory_region_present(MemoryRegion *parent, hwaddr addr);
> > > diff --git a/memory.c b/memory.c
> > > index 59ecc28..3f1df23 100644
> > > --- a/memory.c
> > > +++ b/memory.c
> > > @@ -1562,7 +1562,7 @@ static FlatRange *flatview_lookup(FlatView *view,
> > > AddrRange addr)
> > > bool memory_region_present(MemoryRegion *parent, hwaddr addr)
> > > {
> > > MemoryRegion *mr = memory_region_find(parent, addr, 1).mr;
> > > - if (!mr) {
> > > + if (!mr || (mr == parent)) {
> > > return false;
> > > }
> > > memory_region_unref(mr);
> > > --
> > > 1.7.1
