linux-kernel - Re: [PATCH v2] x86/boot: Use EFI setup data if provided

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Message-ID: <20190328064343.GA1877@MiWiFi-R3L-srv>
Date:   Thu, 28 Mar 2019 14:43:43 +0800
From:   "bhe@...hat.com" <bhe@...hat.com>
To:     Junichi Nomura <j-nomura@...jp.nec.com>
Cc:     Borislav Petkov <bp@...en8.de>, Dave Young <dyoung@...hat.com>,
        "fanc.fnst@...fujitsu.com" <fanc.fnst@...fujitsu.com>,
        "kasong@...hat.com" <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 v2] x86/boot: Use EFI setup data if provided

On 03/28/19 at 04:17am, Junichi Nomura wrote:
> On 2019/03/27 10:48, bhe@...hat.com wrote:
> >>> So efi_get_rsdp_addr() needs to be refactored in such a way so that at
> >>> least the loop towards the end gets carved out into a separate function
> >>> - __efi_get_rsdp_addr() or so - which gets config_tables, nr_tables and
> >>> size as arguments and finds the RSDP address in the kexec-ed kernel.
> >>
> >> You need to carve out the loop at the end and make it into a separate
> >> __efi_get_rsdp_addr() function which gets the physical or the virtual
> >> address.
> > 
> > I guess Boris is suggesting code like below. Please correct me if I am
> > wrong.
> > 
> > static acpi_physical_address _efi_get_rsdp_addr(efi_config_table tbl, ...)
> > {
> > 	/* Get EFI tables from systab. */
> > 	for (i = 0; i < nr_tables; i++) {
> > 		...
> > 	}
> > 	return rsdp_addr;
> > }
> > 
> > static acpi_physical_address efi_get_rsdp_addr(void)
> > {
> > 	...
> > 	/* Get systab from boot params. */		
> > 	...
> > 	/* Handle EFI bitness properly */
> > 	...
> > 	return _efi_get_rsdp_addr();
> > }
> > 
> > 
> > static acpi_physical_address kexec_get_rsdp_addr(void)
> > {
> > 	if (!is_kexec_booted)
> > 		return 0;
> > 
> > 	efi_get_setup_data_addr();
> > 	...
> > 	/* Handle EFI bitness properly */
> > 	...
> > 	return _efi_get_rsdp_addr();
> > }
> 
> I still don't get it... We still need systab for kexec case as well
> to get nr_tables. Don't we?

Yes, simpler.

As Dave replied in another mail, efi/kexec is only added for x86_64. See
how it does in setup_linux_system_parameters() of kexec_tools utility,
and we only have bzImage64 handling in kernel for kexec_file loading,
see prepare_add_efi_setup_data().

You may only need to get kexec ei_info to use directly.

> 
> > acpi_physical_address get_rsdp_addr(void)
> > {
> >          acpi_physical_address pa;
> > 
> >          pa = get_acpi_rsdp();
> > 
> >          if (!pa)
> >                  pa = boot_params->acpi_rsdp_addr;
> > 
> > 
> > 	/**
> > 	/*I think here we should check if it's kexec booted firstly.
> > 	 * Skip it if not kexec. this can avoid the wrong kexec virt
> > 	 * addr parsing./
> >          if (!pa)
> >                  pa = kexec_get_rdsp_addr();             <--- new function
> > 
> >          if (!pa)
> >                  pa = efi_get_rsdp_addr();
> > 
> 
> Shouldn't t efi_get_rsdp_addr() check "is_kexec_booted" and exit
> early so that it never tries to use virtual config_tables pointer
> if for some unknown resason kexec_get_rsdp_addr() failed.

Well, you can just call your efi_get_setup_data_addr() in
kexec_get_rdsp_addr(), if succeed, go ahead to read ei_info and call
_efi_get_rsdp_addr(). If failed, return to try efi_get_rsdp_addr().

> 
> Currently I check "is_kexec_booted" by subset of efi_get_setup_data_addr().
> Do you know a simpler way to check "is_kexec_booted"?

There seems to be no another way to check, I think your way is good.
Tryint to get it in kexec_get_rdsp_addr() earlier, you don't need to
judge specifically in efi_get_rsdp_addr() again.

> 
> >          if (!pa)
> >                  pa = bios_get_rsdp_addr();
> > 
> >          return pa;
> > }
> 
> -- 
> Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.