linux-kernel - Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on kexec-ed kernel

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Date:   Thu, 11 Apr 2019 16:42:35 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Junichi Nomura <j-nomura@...jp.nec.com>
Cc:     Borislav Petkov <bp@...en8.de>, Dave Young <dyoung@...hat.com>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        Kairui Song <kasong@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on
 kexec-ed kernel

On 04/11/19 at 08:16am, Junichi Nomura wrote:
> On 4/11/19 5:09 PM, Borislav Petkov wrote:
> > On Wed, Apr 10, 2019 at 11:34:51PM +0000, Junichi Nomura wrote:
> >> But efi_get_rsdp_addr() needs to check whether the kernel was
> >> kexec booted to avoid accessing invalid EFI table address.
> >> efi_get_kexec_setup_data_addr() is the only method I know
> >> to check if it was kexec-booted.
> > 
> > Your v3 had the right approach - you first check if you can get the
> > address as a kexec-ed kernel. If you do, you use that one and continue
> > the normal path.
> > 
> > If you don't, you fall back to efi_get_rsdp_addr() and get it directly
> > from EFI.
> > 
> > And then carve out the functionality you need to call multiple times in
> > helper functions like __efi_get_rsdp_addr().
> > 
> > Why doesn't that work anymore?
> 
> kexec_get_rsdp_addr() might fail on kexec-booted kernel, e.g. if the
> setup_data was invalid. In such a case, falling back to efi_get_rsdp_addr()
> will hit the problem of accessing invalid table pointer again.

Seems you are trying to address Dave Young's comment in 
http://lkml.kernel.org/r/20190404073233.GC5708@dhcp-128-65.nay.redhat.com

We may need discuss and make clear if those are doable. E.g the first
comment, if not hang by below line of code, returning 0 for what? Can
kexec still be saved, or just reset to firmware?

	error("EFI system table not found in kexec boot_params.")

It may need be clarified firstly, then go further to rearrange patch.
That can ease the work, I guess.

Personal opinion.

Thanks
Baoquan