Re: [PATCH]kdump: pass noefi and acpi_rsdp= to 2nd kernel

[Dave Young <dyoung@redhat.com>]

On 09/06/2012 07:09 AM, Khalid Aziz wrote:

> This will evaluate only the first line in systab. I do not believe you
> are guaranteed to see ACPI20= or ACPI= in the first line. Here is the
> systab file from my machine:
> 
> MPS=0xf4cf0
> ACPI20=0xcac3e000
> ACPI=0xcac3e000
> SMBIOS=0xcac4cf98
> 
> We need to parse all the lines in systab.


Thanks for the reporting, will address this in the update patch

> I think running a kexec/kdump kernel with "noefi" is not a good idea.
> Today kernel makes very little use of UEFI run time services but this
> might change shortly. I have already seen ideas being proposed to use
> UEFI variables to store kernel panic information which would require
> accessing UEFI runtime services. If the kdump kernel runs into a panic,
> it would be good to be able to use UEFI variables to store some sort of
> tombstone. We might also start using UEFI runtime clock services one of
> these days especially now that all PCs soon will have UEFI due to
> Windows 8 requirements. There might be other ways to deal with EFI
> virtualization issue. I have solved it on a custom ia64 kernel by
> passing the kexec'd kernel a "kexec_reboot" on command line, although I
> wouldn't recommend that approach as a general approach. Creating a new
> kernel command line parameter just to tell the kernel to not virtualize
> EFI sounds excessive. May be we can come up with a different way to tell
> a kexec/kdump kernel to not virtualize EFI, like create a new signature,
> for example "EL32_KEXEC" and "EL64_KEXEC", for
> boot_params.efi_info.efi_loader_signature which tells the kexec/kdump
> kernel to enable EFI but skip the step of virtualizing it. More work
> will be needed to make this work, for example pass the EFI runtime
> service memory map from one kernel to the next so we keep it mapped in
> exact same spot, and other similar mapping issues.
> 


I'm not so familiar with uefi detail, is the virtualization issue mean
"virtual mode" of efi?  From my understanding for kdump kernel I would
vote for not interacting with bios at all. We have use "noefi" for long
time by passing it to 2nd kernel while kexecing. I prefer to do this way
until we have to switch to other approach.

-- 
Thanks
Dave

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