linux-kernel - Re: [PATCH v4 2/3] ACPI / NUMA: Add warning message if the padding size for KASLR is not enough

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Message-ID: <20180928024857.GA14470@MiWiFi-R3L-srv>
Date:   Fri, 28 Sep 2018 10:48:57 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Masayoshi Mizuma <msys.mizuma@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] ACPI / NUMA: Add warning message if the padding
 size for KASLR is not enough

On 09/27/18 at 04:31pm, Masayoshi Mizuma wrote:
> From: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
> 
> Add warning message if the padding size for KASLR,
> rand_mem_physical_padding, is not enough. The message also
> says the suitable padding size.
> 
> Signed-off-by: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
> ---
>  arch/x86/include/asm/setup.h |  2 ++
>  drivers/acpi/numa.c          | 14 ++++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
> index ae13bc9..65a5bf8 100644
> --- a/arch/x86/include/asm/setup.h
> +++ b/arch/x86/include/asm/setup.h
> @@ -80,6 +80,8 @@ static inline unsigned long kaslr_offset(void)
>  	return (unsigned long)&_text - __START_KERNEL;
>  }
>  
> +extern int rand_mem_physical_padding;
> +
>  /*
>   * Do NOT EVER look at the BIOS memory size location.
>   * It does not work on many machines.
> diff --git a/drivers/acpi/numa.c b/drivers/acpi/numa.c
> index 8516760..9c3cc3c 100644
> --- a/drivers/acpi/numa.c
> +++ b/drivers/acpi/numa.c
> @@ -32,6 +32,7 @@
>  #include <linux/numa.h>
>  #include <linux/nodemask.h>
>  #include <linux/topology.h>
> +#include <asm/setup.h>
>  
>  static nodemask_t nodes_found_map = NODE_MASK_NONE;
>  
> @@ -435,6 +436,8 @@ acpi_table_parse_srat(enum acpi_srat_type id,
>  int __init acpi_numa_init(void)
>  {
>  	int cnt = 0;
> +	u32 max_phys_addr_tb;
> +	u64 max_phys_addr;
>  
>  	if (acpi_disabled)
>  		return -EINVAL;
> @@ -463,6 +466,17 @@ int __init acpi_numa_init(void)
>  
>  		cnt = acpi_table_parse_srat(ACPI_SRAT_TYPE_MEMORY_AFFINITY,
>  					    acpi_parse_memory_affinity, 0);
> +
> +		if (parsed_numa_memblks && kaslr_enabled()) {
> +			max_phys_addr = PFN_PHYS(max_possible_pfn);
> +			max_phys_addr_tb = (roundup(max_phys_addr, 1ULL << 40)) >> 40;
> +
> +			if (max_phys_addr_tb > rand_mem_physical_padding)

Here I assume max_phys_addr_tb is the end of the possible RAM in system.
rand_mem_physical_padding is the preserved space for later memory
extending. Don't we add the actual RAM size to the
rand_mem_physical_padding, then compare with max_phys_addr_tb?

Please correct me if I am wrong.

Thanks
Baoquan

> +				pr_warn("Set 'rand_mem_physical_padding=%d' "
> +					"as the kernel parameter. "
> +					"Otherwise, memory hotadd may be failed.\n",
> +					max_phys_addr_tb);
> +		}
>  	}
>  
>  	/* SLIT: System Locality Information Table */
> -- 
> 2.18.0
>