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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id w79-v6sm8692194qkw.35.2018.08.21.09.03.58 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 Aug 2018 09:03:59 -0700 (PDT) Subject: Re: [RESEND] [PATCH 1/2] x86/mm: Add an option to change the padding used for the physical memory mapping. To: bhe@redhat.com Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, m.mizuma@jp.fujitsu.com, linux-kernel@vger.kernel.org References: <20180821132401.14563-1-msys.mizuma@gmail.com> <20180821145140.GD29313@MiWiFi-R3L-srv> From: Masayoshi Mizuma Message-ID: Date: Tue, 21 Aug 2018 12:03:58 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180821145140.GD29313@MiWiFi-R3L-srv> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Baoquan, On 08/21/2018 10:51 AM, Baoquan He wrote: > Hi Masa, > > On 08/21/18 at 09:24am, Masayoshi Mizuma wrote: >> From: Masayoshi Mizuma >> >> There are some exceptional cases that the padding used for the physical >> memory mapping section is not enough. >> >> For example of the cases: >> - As Baoquan reported in the following, SGI UV system. >> https://lkml.org/lkml/2017/9/7/87 >> - Each node of physical memory layout has huge space for hotplug. >> For exapmle of the layout: >> SRAT: Node 6 PXM 4 [mem 0x100000000000-0x13ffffffffff] hotplug >> SRAT: Node 7 PXM 5 [mem 0x140000000000-0x17ffffffffff] hotplug >> SRAT: Node 2 PXM 6 [mem 0x180000000000-0x1bffffffffff] hotplug >> SRAT: Node 3 PXM 7 [mem 0x1c0000000000-0x1fffffffffff] hotplug >> >> We can increase the padding by CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING, >> however, the available entropy is decreased if the padding is increased. >> So the config change is not very good for the other most of systems. >> And, the needed padding size depends on the system environment, for >> example physical memory layout, so the kernel option is better than >> changing the config. >> >> Signed-off-by: Masayoshi Mizuma >> --- >> arch/x86/mm/kaslr.c | 20 +++++++++++++++++++- >> 1 file changed, 19 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c >> index 61db77b..8c7b4f6 100644 >> --- a/arch/x86/mm/kaslr.c >> +++ b/arch/x86/mm/kaslr.c >> @@ -33,6 +33,9 @@ >> >> #define TB_SHIFT 40 > > I think this fix makes sense. Since we usually compiled in hotplug code > by default, while may not really hot plug a memory board on most of > systems. However on those systems which really need do hot plug, and > might plug memory board onto physical position above 10TB, this will > cause issues. > > One tiny concern is that we have below definition for 5-level, means we > can only have 4PB of system RAM for now. Not sure if one day it will be > enlarged to 32PB as Documentation/x86/x86_64/mm.txt tell. > > # define MAX_PHYSMEM_BITS (pgtable_l5_enabled() ? 52 : 46) Thank you for pointing it out. I will change the max padding as follows and post v2 patch. static int __init rand_mem_physical_padding_setup(char *str) { int max_padding = (1 <<(MAX_PHYSMEM_BITS - TB_SHIFT)) - 1; > Otherwise this patchset looks good to me. Thank you for your review! - Masa > > Thanks > Baoquan > >> >> +#define MAX_PADDING_L4 63 >> +#define MAX_PADDING_L5 32767 >> + >> /* >> * The end address could depend on more configuration options to make the >> * highest amount of space for randomization available, but that's too hard >> @@ -40,6 +43,7 @@ >> */ >> static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE; >> >> +static int __initdata rand_mem_physical_padding = CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING; >> /* >> * Memory regions randomized by KASLR (except modules that use a separate logic >> * earlier during boot). The list is ordered based on virtual addresses. This >> @@ -69,6 +73,20 @@ static inline bool kaslr_memory_enabled(void) >> return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN); >> } >> >> +static int __init rand_mem_physical_padding_setup(char *str) >> +{ >> + int max_padding = pgtable_l5_enabled() ? MAX_PADDING_L5 : MAX_PADDING_L4; >> + >> + get_option(&str, &rand_mem_physical_padding); >> + if (rand_mem_physical_padding < 0) >> + rand_mem_physical_padding = 0; >> + else if (rand_mem_physical_padding > max_padding) >> + rand_mem_physical_padding = max_padding; >> + >> + return 0; >> +} >> +early_param("rand_mem_physical_padding", rand_mem_physical_padding_setup); >> + >> /* Initialize base and padding for each memory region randomized with KASLR */ >> void __init kernel_randomize_memory(void) >> { >> @@ -102,7 +120,7 @@ void __init kernel_randomize_memory(void) >> */ >> BUG_ON(kaslr_regions[0].base != &page_offset_base); >> memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) + >> - CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING; >> + rand_mem_physical_padding; >> >> /* Adapt phyiscal memory region size based on available memory */ >> if (memory_tb < kaslr_regions[0].size_tb) >> -- >> 2.18.0 >>