linux-kernel - [PATCH v6 3/3] Documentation/kernel-parameters.txt: Document rand_mem_physical

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Date:   Tue,  2 Oct 2018 21:33:23 -0400
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Baoquan He <bhe@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v6 3/3] Documentation/kernel-parameters.txt: Document rand_mem_physical_padding=

This kernel parameter allows the modification of 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         | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 92eb1f4..f0930e3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3529,6 +3529,25 @@
 			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
+			suggests.
+
+			This parameter is useful for memory hot-add capable
+			systems. Such systems may have more space than
+			actual memory size to hot-add memory. If the
+			padding size is not enough and memory is hot-added,
+			the hot-adding will fail because it destroys the
+			system memory map. So, the padding size needs to be
+			adjusted in such a system.
+			The default value is the value of
+			CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING.
+
 	ras=option[,option,...]	[KNL] RAS-specific options
 
 		cec_disable	[X86]
-- 
2.18.0