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

Khalid Aziz khalid at gonehiking.org
Thu Oct 18 15:22:01 EDT 2012

On Thu, 2012-10-18 at 15:11 -0400, Vivek Goyal wrote:
> On Thu, Oct 18, 2012 at 08:56:34AM -0600, Khalid Aziz wrote:
> > On Thu, 2012-10-18 at 11:10 +0800, Dave Young wrote:
> > > 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.
> > > 
> > > Signed-off-by: Dave Young <dyoung at redhat.com>
> > > ---
> > >  kexec/arch/i386/crashdump-x86.c |   35 +++++++++++++++++++++++++++++++++++
> > >  1 file changed, 35 insertions(+)
> > 
> > 
> > Looks good.
> > 
> > Reviewed-by: Khalid Aziz <khalid at gonehiking.org>
> Khalid/Dave,
> Last time khalid mentioned that we are currently taking normal boot path
> in second kernel and that's why things are working even without "noefi"?
> If that's the case, then we don't need "acpi_rsdp" also? In normal boot
> path we used to just pass acpi memmap ranges in e820 map and second
> kernel could find those.
> So now I am full confused that howcome we require acpi_rsdp but not
> "noefi".
> This UEFI thing is a mess. We need to sort it out. I am primarily
> interested in making sure kdump works well with UEFI systems as more
> and more systems are going to adopt UEFI. Also this UEFI secure boot
> will make things very interesting. Now we can't trust the purgatory
> code prepared in user space.
> Thanks
> Vivek

Hi Vivek,

kdump works even without "noefi" because the kdump kernel automatically
boots up with EFI disabled as explained here -
On a BIOS based or EFI based, but with CSM, systems, kdump kernel will
find RSDP by searching through Extended BIOS Data Area. I don't believe
EBDA exists on EFI systems without CSM, so kdump kernel will fail to
find RSDP. We will need to pass "acpi_rsdp=" for the benefit of those
systems, but those systems are also going to need fix in the bootloader
signature to boot kdump kernel in EFI mode.

Yes, UEFI is a mess :) It does need to be sorted out. SecureBoot makes
life even more difficult. Matthew Garret had earlier sent out patches to
support SecureBoot on Linux and one of the things those patches did was
to disable kexec completely. That is a drastic measure and ok as a short
term solution but we need to come up with something better. If
SecureBoot does not go away, we will have to do something in kexec-tools
or even kernel to validate kernel code being loaded for kexec/kdump and
the purgatory code as well. This will require interfacing with UEFI key
checking mechanism. That is going to be ugly.


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