linux-kernel - Re: [PATCH v13 2/6] x86/boot: Introduce get_acpi_rsdp() to parse RSDP in cmdline from KEXEC

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Date:   Fri, 14 Dec 2018 09:32:25 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Masayoshi Mizuma <msys.mizuma@...il.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>,
        <indou.takao@...fujitsu.com>, <caoj.fnst@...fujitsu.com>
Subject: Re: [PATCH v13 2/6] x86/boot: Introduce get_acpi_rsdp() to parse
 RSDP in cmdline from KEXEC

On Thu, Dec 13, 2018 at 02:25:30PM -0500, Masayoshi Mizuma wrote:
>Hi Chao,
>
>Great work! Let me say some trivial comments.

Thanks for your help, any comments will be welcome.

>
>On Wed, Dec 12, 2018 at 11:10:49AM +0800, Chao Fan wrote:
>> Memory information in SRAT is necessary to fix the conflict between
>> KASLR and memory-hotremove.
>> 
>> ACPI SRAT (System/Static Resource Affinity Table) shows the details
>> about memory ranges, including ranges of memory provided by hot-added
>> memory devices. SRAT is introduced by Root System Description
>> Pointer(RSDP). So RSDP should be found firstly.
>> 
>> When booting form KEXEC/EFI/BIOS, the methods to find RSDP
>> are different. When booting from KEXEC, 'acpi_rsdp' may have been
>> added to cmdline, so parse cmdline to find RSDP.
>> 
>> Since 'RANDOMIZE_BASE' && 'MEMORY_HOTREMOVE' is needed, introduce
>> 'CONFIG_EARLY_PARSE_RSDP' to make ifdeffery clear.
>> 
>> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
>> ---
>>  arch/x86/Kconfig                | 10 ++++++++++
>>  arch/x86/boot/compressed/acpi.c | 30 ++++++++++++++++++++++++++++++
>>  arch/x86/boot/compressed/misc.h |  6 ++++++
>>  3 files changed, 46 insertions(+)
>>  create mode 100644 arch/x86/boot/compressed/acpi.c
>> 
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index ba7e3464ee92..455da382fa9e 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -2149,6 +2149,16 @@ config X86_NEED_RELOCS
>>  	def_bool y
>>  	depends on RANDOMIZE_BASE || (X86_32 && RELOCATABLE)
>>  
>> +config EARLY_PARSE_RSDP
>> +	bool "Parse RSDP pointer on compressed period for KASLR"
>> +	def_bool y
>> +	depends on RANDOMIZE_BASE && MEMORY_HOTREMOVE
>> +	help
>> +	  This option parses RSDP in compressed period. Works
>> +	  for KASLR to get memory information from SRAT table and choose
>> +	  immovable memory to extract kernel.
>> +	  Say Y if you want to use both KASLR and memory-hotremove.
>> +
>>  config PHYSICAL_ALIGN
>>  	hex "Alignment value to which kernel should be aligned"
>>  	default "0x200000"
>> diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
>> new file mode 100644
>> index 000000000000..cad15686f82c
>> --- /dev/null
>> +++ b/arch/x86/boot/compressed/acpi.c
>> @@ -0,0 +1,30 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +#define BOOT_CTYPE_H
>> +#include "misc.h"
>> +#include "error.h"
>> +
>> +#include <linux/efi.h>
>> +#include <linux/numa.h>
>> +#include <linux/acpi.h>
>> +#include <asm/efi.h>
>> +
>> +#define STATIC
>> +#include <linux/decompress/mm.h>
>> +
>> +#include "../string.h"
>> +
>> +static acpi_physical_address get_acpi_rsdp(void)
>> +{
>> +#ifdef CONFIG_KEXEC
>> +	unsigned long long res;
>> +	int len = 0;
>> +	char val[MAX_ADDRESS_LENGTH+1];
>> +
>
>> +	len = cmdline_find_option("acpi_rsdp", val, MAX_ADDRESS_LENGTH+1);
>
>sizeof() is better here.
>
>	len = cmdline_find_option("acpi_rsdp", val, sizeof(var));
>
>> +	if (len > 0) {
>> +		val[len] = 0;
>
>'\0' should be fine here not 0.
>
>		val[len] = '\0';
Will change it.

Thanks,
Chao Fan
>
>> +		return (acpi_physical_address)kstrtoull(val, 16, &res);
>> +	}
>> +	return 0;
>> +#endif
>> +}
>> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
>> index a1d5918765f3..72fcfbfec3c6 100644
>> --- a/arch/x86/boot/compressed/misc.h
>> +++ b/arch/x86/boot/compressed/misc.h
>> @@ -116,3 +116,9 @@ static inline void console_init(void)
>>  void set_sev_encryption_mask(void);
>>  
>>  #endif
>> +
>> +/* acpi.c */
>> +#ifdef CONFIG_EARLY_PARSE_RSDP
>> +/* Max length of 64-bit hex address string is 18, prefix "0x" + 16 hex digit. */
>> +#define MAX_ADDRESS_LENGTH 18
>> +#endif
>> -- 
>> 2.19.2
>> 
>> 
>
>