Re: [Xen-devel] [PATCH v6 12/22] arm/acpi: Prepare EFI memory descriptor for Dom0

[Julien Grall <julien.grall@xxxxxxx>]

Hi Shannon,

On 22/03/16 13:16, Shannon Zhao wrote:
> On 2016年03月22日 00:51, Julien Grall wrote:
> > > +        memory_map[offset].Attribute = EFI_MEMORY_WB;
> > > +    }
> > > +
> > > +    for( i = 0; i < acpi_mem.nr_banks; i++, offset++ )
> > > +    {
> > > +        memory_map[offset].Type = EfiACPIReclaimMemory;
> > > +        memory_map[offset].PhysicalStart = acpi_mem.bank[i].start;
> > > +        memory_map[offset].NumberOfPages =
> > > PFN_UP(acpi_mem.bank[i].size);
> > Ditto
> >
> > You are also assuming that acpi_mem.bank[i].size will always be aligned
> > to 4KB. If so, we may expose unwanted data to the guest.
> >
> > Based on how the field is set, I would add a BUG_ON to ensure this
> > condition.
> UEFI spec says
> "EFI memory descriptors of type EfiACPIReclaimMemory and
> EfiACPIMemoryNVS must be aligned on a 4 KiB boundary and must be a
> multiple of 4 KiB in size."
>
> So I think the size is aligned to 4kb, right?
Right. I was suggested to add a BUG_ON to document the constraint and 
ensure nobody will play with acpi_mem outside EFI.
A such check would also be nice for mem->bank[i].size;

Regards,

--
Julien Grall

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