[PATCH v2] kdump: pass acpi_rsdp= to 2nd kernel for efi booting

[Vivek Goyal]

On Thu, Oct 18, 2012 at 02:20:46PM -0700, Eric W. Biederman wrote:
> Dave Young <dyoung at redhat.com> writes:
> 
> > In case efi booting, kdump need kernel parameter acpi_rsdp= to retrieve
> > the acpi root table physical address.
> >
> > Add a function cmdline_add_efi to get the address from /sys/firmware/efi/systab
> > If there's no such file or read fail the function will just do nothing.
> >
> > Tested efi boot Fedora 17 on thinkpad T420.
> >
> > Some background info for this issue:
> > http://lists.infradead.org/pipermail/kexec/2010-March/003889.html
> >
> > [v1 -> v2]:
> > Address comments from Khalid and Simon
> > use fgets instead of read(2) to iterate the file
> > do not add 'noefi' because kexec does not construct EFI signature
> > in bootloader signature in boot_params, so kexec'd kernel will
> > disable EFI automatically even without noefi.
> 
> I don't have any problems with this patch.
> 
> I have a question.  In the case where this fails are we successfully
> passing the ACPI sections in the e820 map?

For kdump we pass everything on commandline using memmap=. This also
includes passing ACPI regions. I don't think we exclude those memmap=
options for EFI.

Also I am wondering that for kdump case why are we passing new memory
map using command line which ultimately overides the e820 map we put
into bootparams.

It should make sense to just put modified map in e820 map in bootparam
and not append all these options on command line. Also simplifiying
the command line. 

This is orthogonal to question you asked but I think this is one
improvement we should do for kexec on panic code.

> 
> If we are passing the acpi sections is that not enough for the kernel
> to find the rdsp area?  I'm just a bit surprised we need this patch
> is all.
> 
> Somehow it seems a bit ugly to pass information that could be conveyed
> in the memory map on the command line.

I have no idea how UEFI case is working. Dave/Khalid might have more
details on this.

Thanks
Vivek