linux-kernel - Re: [PATCH v14 2/5] x86/boot: Introduce efi_get_rsdp

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Message-ID: <20181217173032.GB90818@gmail.com>
Date:   Mon, 17 Dec 2018 18:30:32 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, bp@...en8.de,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        keescook@...omium.org, bhe@...hat.com, msys.mizuma@...il.com,
        indou.takao@...fujitsu.com, caoj.fnst@...fujitsu.com
Subject: Re: [PATCH v14 2/5] x86/boot: Introduce efi_get_rsdp_addr() to find
 RSDP from EFI table


* Chao Fan <fanc.fnst@...fujitsu.com> wrote:

> Memory information in SRAT is necessary to fix the conflict between
> KASLR and memory-hotremove. So RSDP and SRAT should be parsed.
> 
> When booting form KEXEC/EFI/BIOS, the methods to compute RSDP
> are different. When booting from EFI, EFI table points to RSDP.
> So parse the EFI table and find the RSDP.
> 
> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
> ---
>  arch/x86/boot/compressed/acpi.c | 79 +++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
> index 44f19546c169..4151881d8713 100644
> --- a/arch/x86/boot/compressed/acpi.c
> +++ b/arch/x86/boot/compressed/acpi.c
> @@ -28,3 +28,82 @@ static acpi_physical_address get_acpi_rsdp(void)
>  #endif
>  	return 0;
>  }
> +
> +/* Search EFI table for RSDP. */
> +static acpi_physical_address efi_get_rsdp_addr(void)
> +{
> +	acpi_physical_address rsdp_addr = 0;
> +#ifdef CONFIG_EFI
> +	efi_system_table_t *systab;
> +	struct efi_info *e;

'e' is pretty meaningless, the canonical name for efi_info local 
variables is typically 'ei' (although this is not consistent across the 
code).

> +	bool efi_64;

Is this a flag that shows whether the EFI loader is 64-bit?

> +	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 0;
> +	}
> +
> +	/* 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));
> +#else
> +	if (e->efi_systab_hi || e->efi_memmap_hi) {
> +		debug_putstr("Error getting RSDP address: EFI system table located above 4GB.\n");
> +		return 0;
> +	}
> +	systab = (efi_system_table_t *)e->efi_systab;
> +#endif
> +
> +	if (!systab)
> +		return 0;

Is it normal that EFI provides no 'systab'?

> +	/*
> +	 * Get EFI tables from systab. Based on efi_config_init() and
> +	 * efi_config_parse_tables().
> +	 */
> +	size = efi_64 ? sizeof(efi_config_table_64_t) :
> +			sizeof(efi_config_table_32_t);
> +
> +	for (i = 0; i < systab->nr_tables; i++) {
> +		void *config_tables;
> +		unsigned long table;
> +		efi_guid_t guid;
> +
> +		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;

Since 'config_tables' is a void * there's no need to cast the type.

> +			guid = tmp_table->guid;
> +			table = tmp_table->table;
> +
> +			if (!IS_ENABLED(CONFIG_X86_64) && table >> 32) {
> +				debug_putstr("Error getting RSDP address: EFI config table located above 4GB.\n");
> +				return 0;
> +			}
> +		} else {
> +			efi_config_table_32_t *tmp_table;
> +
> +			tmp_table = (efi_config_table_32_t *)config_tables;

Ditto.

> +			guid = tmp_table->guid;
> +			table = tmp_table->table;
> +		}

So it looks like 

> +
> +		if (!(efi_guidcmp(guid, ACPI_TABLE_GUID)))
> +			rsdp_addr = (acpi_physical_address)table;
> +		else if (!(efi_guidcmp(guid, ACPI_20_TABLE_GUID)))
> +			return (acpi_physical_address)table;

'return' is not a function.

Thanks,

	Ingo