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From: Dave Young <dyoung@redhat.com>
Date: Tue, 4 Jun 2024 19:09:56 +0800
Message-ID: <CALu+AoS=-=PbMRxC-1rpfSTPpMOmM5BGRBjLhDwgOC3=4C71ng@mail.gmail.com>
Subject: Re: [PATCH v7 1/3] efi/x86: Fix EFI memory map corruption with kexec
To: Borislav Petkov <bp@alien8.de>
Cc: Mike Rapoport <rppt@kernel.org>, "Kalra, Ashish" <ashish.kalra@amd.com>, tglx@linutronix.de, 
	mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, 
	rafael@kernel.org, hpa@zytor.com, peterz@infradead.org, 
	adrian.hunter@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, 
	jun.nakajima@intel.com, rick.p.edgecombe@intel.com, thomas.lendacky@amd.com, 
	michael.roth@amd.com, seanjc@google.com, kai.huang@intel.com, bhe@redhat.com, 
	kirill.shutemov@linux.intel.com, bdas@redhat.com, vkuznets@redhat.com, 
	dionnaglaze@google.com, anisinha@redhat.com, jroedel@suse.de, ardb@kernel.org, 
	kexec@lists.infradead.org, linux-coco@lists.linux.dev, 
	linux-kernel@vger.kernel.org
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On Tue, 4 Jun 2024 at 17:44, Borislav Petkov <bp@alien8.de> wrote:
>
> On Tue, Jun 04, 2024 at 09:23:58AM +0800, Dave Young wrote:
> > kexec_in_progress is only for checking if this is in a reboot (kexec) code path.
> > But eif_mem_reserve is only called during the boot time so checking
> > kexec_in_progress is meaningless here.
> > current_kernel_is_booted_via_kexec != is_rebooting_with_kexec
>
> That's exactly what I wanna check: whether this is a kexec-ed kernel. Or
> is there a better helper for that?

No general way to check if it is a kexec-ed kernel or not,  for x86
one can check the efi_setup as Ashish's original patch did, as the
kexec booted kernel (efi boot) will have efi setup_data passed in.

Otherwise there is a type_of_loader field for x86 boot protocol,
kexec-tools is 0x0D, the kexec_file_load also uses this.  But adding
the type_of_loader was only added in kexec-tools code when Yinghai
worked on the kexec-tools bzImage64 load, so older kexec-tools will
not set this field.  Anyway the in-kernel kexec_file_load code for x86
added 0x0D as loader type from the beginning.

Anyway there is not such a helper for all cases.

>
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
>