From 9ca5c8e632ce8f144ec6d00da2dc5e16b41d593c Mon Sep 17 00:00:00 2001
From: Dave Young <dyoung@redhat.com>
Date: Sun, 21 Apr 2019 11:50:59 +0800
Subject: x86/kdump: Have crashkernel=X reserve under 4G by default

The kdump crashkernel low reservation is limited to under 896M even for
X86_64. This obscure and miserable limitation exists for compatibility
with old kexec-tools but the reason is not documented anywhere.

Some more tests/investigations about the background:

a) Previously, old kexec-tools could only load purgatory to memory under
   2G. Eric removed that limitation in 2012 in kexec-tools:

     b4f9f8599679 ("kexec x86_64: Make purgatory relocatable anywhere
		   in the 64bit address space.")

b) Back in 2013 Yinghai removed all the limitations in new kexec-tools,
   bzImage64 can be loaded anywhere:

     82c3dd2280d2 ("kexec, x86_64: Load bzImage64 above 4G")

c) Test results with old kexec-tools with old and latest kernels:

  1. Old kexec-tools can not build with modern toolchain anymore,
     I built it in a RHEL6 vm.

  2. 2.0.0 kexec-tools does not work with the latest kernel even with
     memory under 896M and gives an error:

     "ELF core (kcore) parse failed"

     For that it needs below kexec-tools fix:

       ed15ba1b9977 ("build_mem_phdrs(): check if p_paddr is invalid")

  3. Even with patched kexec-tools which fixes 2),  it still needs some
     other fixes to work correctly for KASLR-enabled kernels.

So the situation is:

* Old kexec-tools is already broken with latest kernels.

* We can not keep these limitations forever just for compatibility with very
  old kexec-tools.

* If one must use old tools then he/she can choose crashkernel=X@Y.

* People have reported bugs where crashkernel=384M failed because KASLR
  makes the 0-896M space sparse.

* Crashkernel can reserve in low or high area, it is natural to understand
  low as memory under 4G.

Hence drop the 896M limitation and change crashkernel low reservation to
reserve under 4G by default.

Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Petr Tesarik <ptesarik@suse.cz>
Cc: piliu@redhat.com
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Sinan Kaya <okaya@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: vgoyal@redhat.com
Cc: x86-ml <x86@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Zhimin Gu <kookoo.gu@intel.com>
Link: https://lkml.kernel.org/r/20190421035058.943630505@redhat.com
---
 arch/x86/kernel/setup.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3d872a527cd9..daf7c5650c18 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -71,6 +71,7 @@
 #include <linux/tboot.h>
 #include <linux/jiffies.h>
 #include <linux/mem_encrypt.h>
+#include <linux/sizes.h>
 
 #include <linux/usb/xhci-dbgp.h>
 #include <video/edid.h>
@@ -448,18 +449,17 @@ static void __init memblock_x86_reserve_range_setup_data(void)
 #ifdef CONFIG_KEXEC_CORE
 
 /* 16M alignment for crash kernel regions */
-#define CRASH_ALIGN		(16 << 20)
+#define CRASH_ALIGN		SZ_16M
 
 /*
  * Keep the crash kernel below this limit.  On 32 bits earlier kernels
  * would limit the kernel to the low 512 MiB due to mapping restrictions.
- * On 64bit, old kexec-tools need to under 896MiB.
  */
 #ifdef CONFIG_X86_32
-# define CRASH_ADDR_LOW_MAX	(512 << 20)
-# define CRASH_ADDR_HIGH_MAX	(512 << 20)
+# define CRASH_ADDR_LOW_MAX	SZ_512M
+# define CRASH_ADDR_HIGH_MAX	SZ_512M
 #else
-# define CRASH_ADDR_LOW_MAX	(896UL << 20)
+# define CRASH_ADDR_LOW_MAX	SZ_4G
 # define CRASH_ADDR_HIGH_MAX	MAXMEM
 #endif
 
-- 
cgit v1.2.3-59-g8ed1b


From b9ac3849af412fd3887d7652bdbabf29d2aecc16 Mon Sep 17 00:00:00 2001
From: Dave Young <dyoung@redhat.com>
Date: Mon, 22 Apr 2019 11:19:05 +0800
Subject: x86/kdump: Fall back to reserve high crashkernel memory

crashkernel=xM tries to reserve memory for the crash kernel under 4G,
which is enough, usually. But this could fail sometimes, for example
when one tries to reserve a big chunk like 2G, for example.

So let the crashkernel=xM just fall back to use high memory in case it
fails to find a suitable low range. Do not set the ,high as default
because it allocates extra low memory for DMA buffers and swiotlb, and
this is not always necessary for all machines.

Typically, crashkernel=128M usually works with low reservation under 4G,
so keep <4G as default.

 [ bp: Massage. ]

Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: linux-doc@vger.kernel.org
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Petr Tesarik <ptesarik@suse.cz>
Cc: piliu@redhat.com
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Sinan Kaya <okaya@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thymo van Beers <thymovanbeers@gmail.com>
Cc: vgoyal@redhat.com
Cc: x86-ml <x86@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Zhimin Gu <kookoo.gu@intel.com>
Link: https://lkml.kernel.org/r/20190422031905.GA8387@dhcp-128-65.nay.redhat.com
---
 Documentation/admin-guide/kernel-parameters.txt |  7 +++++--
 arch/x86/kernel/setup.c                         | 22 ++++++++++++++--------
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..24d01648edeb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -704,8 +704,11 @@
 			upon panic. This parameter reserves the physical
 			memory region [offset, offset + size] for that kernel
 			image. If '@offset' is omitted, then a suitable offset
-			is selected automatically. Check
-			Documentation/kdump/kdump.txt for further details.
+			is selected automatically.
+			[KNL, x86_64] select a region under 4G first, and
+			fall back to reserve region above 4G when '@offset'
+			hasn't been specified.
+			See Documentation/kdump/kdump.txt for further details.
 
 	crashkernel=range1:size1[,range2:size2,...][@offset]
 			[KNL] Same as above, but depends on the memory
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index daf7c5650c18..c15f362a2516 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -541,21 +541,27 @@ static void __init reserve_crashkernel(void)
 	}
 
 	/* 0 means: find the address automatically */
-	if (crash_base <= 0) {
+	if (!crash_base) {
 		/*
 		 * Set CRASH_ADDR_LOW_MAX upper bound for crash memory,
-		 * as old kexec-tools loads bzImage below that, unless
-		 * "crashkernel=size[KMG],high" is specified.
+		 * crashkernel=x,high reserves memory over 4G, also allocates
+		 * 256M extra low memory for DMA buffers and swiotlb.
+		 * But the extra memory is not required for all machines.
+		 * So try low memory first and fall back to high memory
+		 * unless "crashkernel=size[KMG],high" is specified.
 		 */
-		crash_base = memblock_find_in_range(CRASH_ALIGN,
-						    high ? CRASH_ADDR_HIGH_MAX
-							 : CRASH_ADDR_LOW_MAX,
-						    crash_size, CRASH_ALIGN);
+		if (!high)
+			crash_base = memblock_find_in_range(CRASH_ALIGN,
+						CRASH_ADDR_LOW_MAX,
+						crash_size, CRASH_ALIGN);
+		if (!crash_base)
+			crash_base = memblock_find_in_range(CRASH_ALIGN,
+						CRASH_ADDR_HIGH_MAX,
+						crash_size, CRASH_ALIGN);
 		if (!crash_base) {
 			pr_info("crashkernel reservation failed - No suitable area found.\n");
 			return;
 		}
-
 	} else {
 		unsigned long long start;
 
-- 
cgit v1.2.3-59-g8ed1b