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

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb64470d0d6d6ccadccf8b8fbbf86509d..24d01648edeb1ec09c3140d56e86ab2486b09d4b 100644 (file)
--- 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 daf7c5650c18c8d28f27e1c881fd849b6dd41b07..c15f362a251681007131ef435ba83273b08f0562 100644 (file)
--- 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;