Re: [PATCH v11 1/5] x86/boot: Add efi_get_rsdp_addr() to dig out RSDP from EFI table

[Borislav Petkov]

On Mon, Nov 12, 2018 at 05:46:41PM +0800, Chao Fan wrote:
> In order to parse SRAT table and get memory information, RSDP pointer
> should be found. In kernel, there are three methods to get RSDP:
> EFI condition, BIOS condition and KEXEC condition. The first works
> for EFI condition.

"condition"?

Also, please explain shortly what all those abbreviations mean: think
of a person reading your commit message who doesn't have any clue from
ACPI.

> Imitate ACPI code and EFI code to dig RSDP pointer from EFI tables.
> Process: boot_param->systab->efi_config_table->RSDP.
> Based on efi_init(), efi_config_init(), efi_config_parse_tables().
> 
> Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/acpitb.c | 96 +++++++++++++++++++++++++++++++
>  1 file changed, 96 insertions(+)
>  create mode 100644 arch/x86/boot/compressed/acpitb.c
> 
> diff --git a/arch/x86/boot/compressed/acpitb.c b/arch/x86/boot/compressed/acpitb.c
> new file mode 100644
> index 000000000000..56b54b0e0889
> --- /dev/null
> +++ b/arch/x86/boot/compressed/acpitb.c
> @@ -0,0 +1,96 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BOOT_CTYPE_H
> +#include "misc.h"
> +#include "error.h"
> +
> +#include <linux/efi.h>
> +#include <asm/efi.h>
> +#include <linux/numa.h>
> +#include <linux/acpi.h>
> +
> +/* Search EFI table for RSDP table. */
> +static void efi_get_rsdp_addr(acpi_physical_address *rsdp_addr)

This is just silly: the function returns void and has a single parameter
which is an *output* parameter?!

Why isn't the signature

static acpi_physical_address *efi_get_rsdp_addr(void)

instead?

> +{
> +#ifdef CONFIG_EFI
> +	efi_system_table_t *systab;
> +	bool efi_64 = false;

You're setting it below already, why here too?

> +	void *config_tables;
> +	struct efi_info *e;
> +	char *sig;
> +	int size;
> +	int i;
> +
> +	e = &boot_params->efi_info;
> +	sig = (char *)&e->efi_loader_signature;
> +
> +	if (!strncmp(sig, EFI64_LOADER_SIGNATURE, 4))
> +		efi_64 = true;
> +	else if (!strncmp(sig, EFI32_LOADER_SIGNATURE, 4))
> +		efi_64 = false;
> +	else {
> +		debug_putstr("Wrong EFI loader signature.\n");
> +		return;
> +	}
> +
> +	/* Get systab from boot params. Based on efi_init(). */
> +#ifdef CONFIG_X86_64
> +	systab = (efi_system_table_t *)(
> +			e->efi_systab | ((__u64)e->efi_systab_hi<<32));

No ugly line breaks with open braces trailing like that, pls - just let
it stick out.

> +#else
> +	if (e->efi_systab_hi || e->efi_memmap_hi) {
> +		debug_putstr("Table located above 4GB. EFI should be disabled.\n");

You need to say here what really happens here:

		debug_putstr("Error getting RSDP address: EFI system table located above 4GB.\n");

The same below.

> +		return;
> +	}
> +	systab = (efi_system_table_t *)e->efi_systab;
> +#endif
> +
> +	if (!systab)
> +		return;
> +
> +	/*
> +	 * Get EFI tables from systab. Based on efi_config_init() and
> +	 * efi_config_parse_tables(). Only dig out the config_table.
> +	 */
> +	size = efi_64 ? sizeof(efi_config_table_64_t) :
> +			sizeof(efi_config_table_32_t);
> +
> +	for (i = 0; i < systab->nr_tables; i++) {
> +		efi_guid_t guid;
> +		unsigned long table;

Put the void *config_tables declaration here.

> +
> +		config_tables = (void *)(systab->tables + size * i);
> +		if (efi_64) {
> +			efi_config_table_64_t *tmp_table;
> +
> +			tmp_table = (efi_config_table_64_t *)config_tables;
> +			guid = tmp_table->guid;
> +			table = tmp_table->table;
> +#ifndef CONFIG_64BIT

Above you have CONFIG_X86_64, here CONFIG_64BIT. Please use one only.

Also, use IS_ENABLED() instead.

> +			if (table >> 32) {
> +				debug_putstr("Table located above 4G. EFI should be disabled.\n");
> +				return;
> +			}
> +#endif
> +		} else {
> +			efi_config_table_32_t *tmp_table;
> +
> +			tmp_table = (efi_config_table_32_t *)config_tables;
> +			guid = tmp_table->guid;
> +			table = tmp_table->table;
> +		}
> +
> +		/*
> +		 * Get RSDP from EFI tables.
> +		 * If ACPI20 table found, use it.
> +		 * If ACPI20 table not found, but ACPI table found,
> +		 * use the ACPI table.
> +		 */

That comment is the opposite of what the code does. Also, why is that
comment needed at all? If anything, it should say *why* ACPI_TABLE_GUID
is preferred and then the fallback to ACPI_20_TABLE_GUID is done - not
*what* it does. That's easily visible in the code.

Thx.

-- 
Regards/Gruss,
    Boris.

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