Re: [Qemu-devel] [PATCH] memory_region_present: return false if address is not found in child MemoryRegion

[Michael S. Tsirkin]

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 <address@hidden>

Hmm, I wonder whether this still should return true
if parent is not a pure container.
Also what if MR isn't under parent at all?

Maybe the right thing to do is
return mr->ops == &unassigned_mem_ops ?


> ---
>  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