linux-kernel - [PATCH v5 3/3] docs: kernel-parameters.txt: document rand_mem_physical

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Date:   Mon,  1 Oct 2018 10:08:43 -0400
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Baoquan He <bhe@...hat.com>
Cc:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v5 3/3] docs: kernel-parameters.txt: document rand_mem_physical_padding

From: Masayoshi Mizuma <m.mizuma@...fujitsu.com>

This kernel parameter allows to change the padding used
for the physical memory mapping section when KASLR
memory is enabled.

For memory hotplug capable systems, the default padding size,
CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING, may not be enough.
The option is useful to adjust the padding size.

Signed-off-by: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
---
 .../admin-guide/kernel-parameters.txt          | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 92eb1f4..4c4c5e6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3529,6 +3529,24 @@
 			fully seed the kernel's CRNG. Default is controlled
 			by CONFIG_RANDOM_TRUST_CPU.
 
+	rand_mem_physical_padding=
+			[KNL] Define the padding size in terabytes
+			used for the physical memory mapping section
+			when KASLR is enabled.
+			If the padding size is not enough, you can see
+			'Set rand_mem_physical_padding=XX ...' in system
+			boot message, so set the parameter as the message.
+
+			This parameter is useful for the memory hot-add capable
+			system. Such system may have more space than
+			actual memory size to hot-add memory. If the
+			padding size is not enough and a memory is hot-added,
+			the hot-adding will fail because it destroys the
+			system memory map. So, the padding size is needed to
+			adjust in such system.
+			The default value is
+			CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING.
+
 	ras=option[,option,...]	[KNL] RAS-specific options
 
 		cec_disable	[X86]
-- 
2.18.0