On Mon, Dec 17, 2018 at 06:25:10PM +0100, Ingo Molnar wrote:
>
>* Chao Fan <fanc.f...@cn.fujitsu.com> 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.
>
>What is the nature of the basic conflict? Should the kernel only allow
>hot-removing memory ranges that are explicitly marked as such in the
>SRAT? I presume that's already so, correct? Or should the kernel avoiding
>KASLR-randomizing into hot-removable memory areas?
The basic conflict is the kernel avoiding KASLR-randomizing into
hot-removable memory areas.
>
>Some minor nits:
>
>> Signed-off-by: Chao Fan <fanc.f...@cn.fujitsu.com>
>> ---
>> arch/x86/boot/compressed/acpi.c | 30 ++++++++++++++++++++++++++++++
>> 1 file changed, 30 insertions(+)
>> create mode 100644 arch/x86/boot/compressed/acpi.c
>>
>> diff --git a/arch/x86/boot/compressed/acpi.c
>> b/arch/x86/boot/compressed/acpi.c
>> new file mode 100644
>> index 000000000000..44f19546c169
>> --- /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>
>> +
>> +/* Max length of 64-bit hex address string is 18, prefix "0x" + 16 hex
>> digits */
>> +#define MAX_ADDRESS_LENGTH 18
>
>I'd suggest adding the +1 for the string termination \0 as well, and use
>that below.
>
>Also, 'max address length' is way too generic (and hence pretty
>meaningless) - how about MAX_HEX_ADDRESS_STRING_LEN or so?
OK, I will change the name and add the \0.
Thanks,
Chao Fan
>
>> +
>> +static acpi_physical_address get_acpi_rsdp(void)
>> +{
>> +#ifdef CONFIG_KEXEC
>> + char val[MAX_ADDRESS_LENGTH+1];
>> + unsigned long long res;
>> + int len;
>> +
>> + len = cmdline_find_option("acpi_rsdp", val, MAX_ADDRESS_LENGTH+1);
>> + if (len > 0) {
>> + char *e;
>> +
>> + val[len] = '\0';
>> + return (acpi_physical_address)simple_strtoull(val, &e, 16);
>
>'return' is not a function - no need for the parenthesis.
>
>Thanks,
>
> Ingo
>
>
