Re: [patch 2/2] /dev/mem validate mmap requests

[Bjorn Helgaas]

On Tuesday 13 December 2005 5:25 pm, Luck, Tony wrote:
> > Tony, can you ack/nak this please?  It touches both ia64 and generic
> > code.
> 
> So if someone tries to mmap a range that spans across more than
> one EFI memory descriptor, the size will get trimmed back to an
> EFI memory boundary.  Isn't that a problem since 1<<EFI_PAGE_SHIFT
> is less than the default ia64 Linux page size?

The EFI page size is smaller than the Linux page size, but firmware
typically coalesces adjacent ranges with the same attributes.

> I think you may need a more complex checker that does aggregation
> of adjacent efi memory descriptors with the same attributes.

We could, but I don't think it's worth it at this point.  We've
been using the same simple-minded scheme for validating /dev/mem
read & write requests for quite a while with no problems, and I
don't want to over-engineer this.

If hot-plug memory is ever finished, the checker may have to
be extended to comprehend regions described by ACPI as well as
those described in the boot-time EFI memory map.  I think that
would be the right time to make it smarter about spanning
descriptors.
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