Re: [PATCH v11 3/5] x86/boot: Add get_acpi_rsdp() to parse RSDP in cmdlien from kexec

Chao Fan
2018-11-14T01:54:50Z

On Tue, Nov 13, 2018 at 06:51:50PM +0100, Borislav Petkov wrote:
>On Mon, Nov 12, 2018 at 05:46:43PM +0800, Chao Fan wrote:
>> Imitate setup_acpi_rsdp() for the early_param of 'acpi_rsdp'.
>> KEXEC writes the RSDP pointer to cmdline for EFI booting.
>> So if 'acpi_rsdp' found in cmdline, use it directely.
>>
>> Since function kstrtoull() is needed, include it in
>> arch/x86/boot/string.h. To solve the definition conflict
>> problem, set BOOT_STRING tag to expose only kstrtoull() and
>> functions used by it. Other functions in lib/kstrtox.c will
>> be covered.
>>
>> Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
>> ---
>> arch/x86/boot/compressed/acpitb.c | 26 ++++++++++++++++++++++++++
>> arch/x86/boot/string.h | 4 ++++
>> lib/kstrtox.c | 4 ++++
>> 3 files changed, 34 insertions(+)
>>
>> diff --git a/arch/x86/boot/compressed/acpitb.c b/arch/x86/boot/compressed/acpitb.c
>> index 50fa65cf824d..5cfb4efa5a19 100644
>> --- a/arch/x86/boot/compressed/acpitb.c
>> +++ b/arch/x86/boot/compressed/acpitb.c
>> @@ -8,6 +8,12 @@
>> #include <linux/numa.h>
>> #include <linux/acpi.h>
>>
>> +#define STATIC
>> +#include <linux/decompress/mm.h>
>> +
>> +#define BOOT_STRING
>> +#include "../string.h"
>> +
>> /* Search EFI table for RSDP table. */
>> static void efi_get_rsdp_addr(acpi_physical_address *rsdp_addr)
>> {
>> @@ -200,3 +206,23 @@ static void bios_get_rsdp_addr(acpi_physical_address *rsdp_addr)
>> *rsdp_addr = (acpi_physical_address)address;
>> }
>> }
>> +
>> +static void get_acpi_rsdp(acpi_physical_address *rsdp_addr)
>> +{
>> +#ifdef CONFIG_KEXEC
>
>Ok, why is that CONFIG_KEXEC dependency needed now too?
>

CONFIG_KEXEC is only needed in this function.

When searching RSDP, there are three methods in order:
1. When booting from KEXEC, 'acpi_rsdp' is added to cmdline by KEXEC,
so it can be parsed and used. CONFIG_KEXEC is needed here.
2. When booting from EFI, parse EFI table and find RSDP.
3. When booting from BIOS, search memory for RSDP just like
acpi_find_root_pointer() in drivers/acpi/acpica/tbxfroot.c did.

So, CONFIG_KEXEC is only needed in 1, exactly in this function
get_acpi_rsdp() of my PATCH.

Thanks,
Chao Fan

>Ok, let's recap: so far, for your use case you need:
>
>CONFIG_MEMORY_HOTREMOVE
>CONFIG_RANDOMIZE_BASE
>and now
>CONFIG_KEXEC
>
>So, you can clean up all that ifdeffery by defining a new config item
>CONFIG_EARLY_PARSE_RSDP or so which depends on all those three items and
>then you can do
>
>vmlinux-objs-$(CONFIG_EARLY_PARSE_RSDP) += $(obj)/acpitb.o
>
>and get rid of the most of the ifdeffery.
>
>Yes?
>
>> + unsigned long long res;
>> + int len = 0;
>> + char *val;
>> +
>> + val = malloc(19);
>> + len = cmdline_find_option("acpi_rsdp", val, 19);
>> +
>
>^ Superfluous newline.
>
>> + if (len == -1)
>> + return;
>
>That check is not needed since you do > 0 below.
>
>> +
>> + if (len > 0) {
>> + val[len] = 0;
>> + *rsdp_addr = (acpi_physical_address)kstrtoull(val, 16, &res);
>> + }
>> +#endif
>> +}
>> diff --git a/arch/x86/boot/string.h b/arch/x86/boot/string.h
>> index 3d78e27077f4..0ff3edb888e4 100644
>> --- a/arch/x86/boot/string.h
>> +++ b/arch/x86/boot/string.h
>> @@ -30,3 +30,7 @@ extern unsigned long long simple_strtoull(const char *cp, char **endp,
>> unsigned int base);
>>
>> #endif /* BOOT_STRING_H */
>> +
>> +#ifdef BOOT_STRING
>> +#include "../../../lib/kstrtox.c"
>> +#endif
>> diff --git a/lib/kstrtox.c b/lib/kstrtox.c
>> index 1006bf70bf74..3804db9eed56 100644
>> --- a/lib/kstrtox.c
>> +++ b/lib/kstrtox.c
>> @@ -126,6 +126,8 @@ int kstrtoull(const char *s, unsigned int base, unsigned long long *res)
>> }
>> EXPORT_SYMBOL(kstrtoull);
>
>This needs a comment to explain what is that guard used for.
>
>> +#ifndef BOOT_STRING
>> +
>> /**
>> * kstrtoll - convert a string to a long long
>> * @s: The start of the string. The string must be null-terminated, and may also
>> @@ -408,3 +410,5 @@ kstrto_from_user(kstrtou16_from_user, kstrtou16, u16);
>> kstrto_from_user(kstrtos16_from_user, kstrtos16, s16);
>> kstrto_from_user(kstrtou8_from_user, kstrtou8, u8);
>> kstrto_from_user(kstrtos8_from_user, kstrtos8, s8);
>> +
>> +#endif
>
>#endif /* BOOT_STRING */
>
>--
>Regards/Gruss,
> Boris.
>
>Good mailing practices for 400: avoid top-posting and trim the reply.
>
>