Re: [PATCH -v2] EFI: Runtime services virtual mapping

Dave Young
2013-09-25T02:36:38Z

On 09/24/13 at 05:12pm, H. Peter Anvin wrote:
> On 09/24/2013 07:56 AM, Borislav Petkov wrote:
> > On Tue, September 24, 2013 2:45 pm, Dave Young wrote:
> >> Think again about this, how about 1:1 map them from a base address
> >> like -64G phy_addr -> (-64G + phy_addr), in this way we can avoid
> >> depending on the previous region size.
> >
> > Right, how we layout the regions is arbitrary as long as we start at
> > the same VA and use the same regions, in the same order and of the same
> > size...
> >
> >> For the zero region problem, we can resolve it as a standalone
> >> problem.
> >
> > ... however, we still need to understand why it fails mapping the boot
> > services region as some implementations apparently do call boot services
> > even after ExitBootServices(). IOW, we need that region mapped in the
> > kexec'ed kernel too.
> >
>
> I am starting to think that we really should explicitly pass along the
> EFI mappings to the secondary kernel. This will also help if we have to
> change the algorithm in a future kernel.

The 0 size mem region is still a problem even we pass the previous mapping
to 2nd kernel. So will be be enough to 1:1 map on high address and leave the
firmware provided memmap not touched, use a copy of memmap in kernel?

>
> The most logical way to do this is to define a new setup_data type and
> pass the entire set of physical-to-virtual mappings that way.
>
> For example:
>
> struct efi_mapping {
> u64 va; /* Virtual start address */
> u64 pa; /* Physical start address */
> u64 len; /* Length in bytes */
> u64 type; /* Mapping type */
> u64 reserved[3]; /* Reserved, must be zero */
> };
>
> Adding some reserved fields seems like a prudent precaution; the map
> shouldn't be all that large anyway.
>
> -hpa
>