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

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Date:   Fri, 29 Mar 2019 03:34:23 +0000
From:   Junichi Nomura <j-nomura@...jp.nec.com>
To:     "bhe@...hat.com" <bhe@...hat.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 3/29/19 8:11 AM, bhe@...hat.com wrote:
> On 03/28/19 at 07:43am, Junichi Nomura wrote:
>>  /* Search EFI system tables for RSDP. */
>> -static acpi_physical_address efi_get_rsdp_addr(void)
>> +static acpi_physical_address __efi_get_rsdp_addr(unsigned long config_tables, unsigned int nr_tables, int size, bool efi_64)
> 
> Here parameter 'size' and 'efi_64' seems a little duplicated on
> functionality. Only passing efi_64 can deduce the size? Personal
> opinion.

Yes. But I'm not sure which is preferred.

The current code is:

__efi_get_rsdp_addr() {
        for (i = 0; i < nr_tables; i++) {
                config_tables += size;
                if (efi_64) {
                        efi_config_table_64_t *tbl = (efi_config_table_64_t *)config_tables;
                        // get guid and table
                } else {
                        efi_config_table_32_t *tbl = (efi_config_table_32_t *)config_tables;
                        // get guid and table
                }
                // check guid and return table if it's valid
        }
}

If we remove "size" parameter, that will become:

__efi_get_rsdp_addr() {
        for (i = 0; i < nr_tables; i++) {
                if (efi_64) {
                        efi_config_table_64_t *tbl;
                        config_tables += sizeof(efi_config_table_64_t);
                        tbl = (efi_config_table_64_t *)config_tables;
                        // get guid and table
                } else {
                        efi_config_table_32_t *tbl;
                        config_tables += sizeof(efi_config_table_32_t);
                        tbl = (efi_config_table_32_t *)config_tables;
                        // get guid and table
                }
                // check guid and return table if it's valid
        }
}

Or we could create 2 functions, __efi_get_rsdp_addr32() and __efi_get_rsdp_addr64(),
and let efi_get_rsdp_addr() to choose which one to use based on signature.

> It might be worth adding code comments here to tell why we only care
> about 64bit kexec booting?

I think so. I'll add a comment.

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