Re: [PATCH] hw/i386/pc: when adding reserved E820 entries do not allocate dynamic entries

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 23 Feb 2022 17:30:34 +0530
Ani Sinha <ani@anisinha.ca> wrote:

> On Wed, Feb 23, 2022 at 2:34 PM Igor Mammedov <imammedo@redhat.com> wrote:
> >
> > On Thu, 10 Feb 2022 18:58:21 +0530
> > Ani Sinha <ani@anisinha.ca> wrote:
> >  
> > > When adding E820_RESERVED entries we also accidentally allocate dynamic
> > > entries. This is incorrect. We should simply return early with the count of
> > > the number of reserved entries added.  
> >
> > can you expand commit message to explain what's wrong and
> > how problem manifests ... etc.  
> 
> The issue has been present for the last 8 years without apparent
> visible issues. I think the only issue is that the bug allocates more
> memory in the firmware than is actually needed.

let me repeat: Why do you think it's an issue or why it's wrong

> 
> >  
> > >
> > > fixes: 7d67110f2d9a6("pc: add etc/e820 fw_cfg file")
> > > cc: kraxel@redhat.com
> > > Signed-off-by: Ani Sinha <ani@anisinha.ca>
> > > ---
> > >  hw/i386/e820_memory_layout.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/hw/i386/e820_memory_layout.c b/hw/i386/e820_memory_layout.c
> > > index bcf9eaf837..afb08253a4 100644
> > > --- a/hw/i386/e820_memory_layout.c
> > > +++ b/hw/i386/e820_memory_layout.c
> > > @@ -31,6 +31,8 @@ int e820_add_entry(uint64_t address, uint64_t length, uint32_t type)
> > >          entry->type = cpu_to_le32(type);
> > >
> > >          e820_reserve.count = cpu_to_le32(index);
> > > +
> > > +        return index;
> > >      }  
> >
> > this changes e820_table size/content, which is added by fw_cfg_add_file() to fwcfg,
> > as result it breaks ABI in case of migration.  
> 
> Ugh. So should we keep the bug? or do we add config setting to handle
> the ABI breakage.
>