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

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Date:   Thu, 28 Mar 2019 14:26:45 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Junichi Nomura <j-nomura@...jp.nec.com>
CC:     "bhe@...hat.com" <bhe@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Young <dyoung@...hat.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 Thu, Mar 28, 2019 at 04:17:16AM +0000, 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?
>
>> 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.

In my understanding, in EFI issue, RSDP is from efi_get_rsdp_addr() or
kexec_get_rdsp_addr()(only in kexec environment). So in these two functions
only one can be excuted, so how about this:

if (is_kexec_booted)
	pa = kexec_get_rdsp_addr();	<--- new function
else
	pa = efi_get_rsdp_addr();

And also split the same code as _efi_get_rsdp_addr().
If there is something wrong in my understanding, please let me know.

Thanks,
Chao Fan

>
>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.
>