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

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Date:   Thu, 28 Mar 2019 04:17:16 +0000
From:   Junichi Nomura <j-nomura@...jp.nec.com>
To:     "bhe@...hat.com" <bhe@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "Dave Young" <dyoung@...hat.com>
CC:     "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 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?

> 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.

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"?

>          if (!pa)
>                  pa = bios_get_rsdp_addr();
> 
>          return pa;
> }

-- 
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.