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* [PATCH] x86: Do not reserve a crash kernel region if booted on Xen PV
@ 2018-04-25 10:08 Petr Tesarik
  2018-04-25 12:53 ` Juergen Gross
  2018-04-27 15:09 ` [tip:x86/urgent] x86/setup: " tip-bot for Petr Tesarik
  0 siblings, 2 replies; 3+ messages in thread
From: Petr Tesarik @ 2018-04-25 10:08 UTC (permalink / raw)
  To: x86, Thomas Gleixner, Ingo Molnar, H. Peter Anvin, Tom Lendacky,
	Borislav Petkov, Juergen Gross, Andy Lutomirski, Mikulas Patocka,
	Jean Delvare, Boris Ostrovsky, Dou Liyang
  Cc: xen-devel, linux-kernel

Xen PV domains cannot shut down and start a crash kernel. Instead,
the crashing kernel makes a SCHEDOP_shutdown hypercall with the
reason code SHUTDOWN_crash, cf. xen_crash_shutdown() machine op in
arch/x86/xen/enlighten_pv.c.

A crash kernel reservation is merely a waste of RAM in this case. It
may also confuse users of kexec_load(2) and/or kexec_file_load(2).
When flags include KEXEC_ON_CRASH or KEXEC_FILE_ON_CRASH,
respectively, these syscalls return success, which is technically
correct, but the crash kexec image will never be actually used.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 arch/x86/kernel/setup.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 6285697b6e56..5c623dfe39d1 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -50,6 +50,7 @@
 #include <linux/init_ohci1394_dma.h>
 #include <linux/kvm_para.h>
 #include <linux/dma-contiguous.h>
+#include <xen/xen.h>
 
 #include <linux/errno.h>
 #include <linux/kernel.h>
@@ -534,6 +535,11 @@ static void __init reserve_crashkernel(void)
 		high = true;
 	}
 
+	if (xen_pv_domain()) {
+		pr_info("Ignoring crashkernel for a Xen PV domain\n");
+		return;
+	}
+
 	/* 0 means: find the address automatically */
 	if (crash_base <= 0) {
 		/*
-- 
2.13.6

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] x86: Do not reserve a crash kernel region if booted on Xen PV
  2018-04-25 10:08 [PATCH] x86: Do not reserve a crash kernel region if booted on Xen PV Petr Tesarik
@ 2018-04-25 12:53 ` Juergen Gross
  2018-04-27 15:09 ` [tip:x86/urgent] x86/setup: " tip-bot for Petr Tesarik
  1 sibling, 0 replies; 3+ messages in thread
From: Juergen Gross @ 2018-04-25 12:53 UTC (permalink / raw)
  To: Petr Tesarik, x86, Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
	Tom Lendacky, Borislav Petkov, Andy Lutomirski, Mikulas Patocka,
	Jean Delvare, Boris Ostrovsky, Dou Liyang
  Cc: xen-devel, linux-kernel

On 25/04/18 12:08, Petr Tesarik wrote:
> Xen PV domains cannot shut down and start a crash kernel. Instead,
> the crashing kernel makes a SCHEDOP_shutdown hypercall with the
> reason code SHUTDOWN_crash, cf. xen_crash_shutdown() machine op in
> arch/x86/xen/enlighten_pv.c.
> 
> A crash kernel reservation is merely a waste of RAM in this case. It
> may also confuse users of kexec_load(2) and/or kexec_file_load(2).
> When flags include KEXEC_ON_CRASH or KEXEC_FILE_ON_CRASH,
> respectively, these syscalls return success, which is technically
> correct, but the crash kexec image will never be actually used.
> 
> Signed-off-by: Petr Tesarik <ptesarik@suse.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [tip:x86/urgent] x86/setup: Do not reserve a crash kernel region if booted on Xen PV
  2018-04-25 10:08 [PATCH] x86: Do not reserve a crash kernel region if booted on Xen PV Petr Tesarik
  2018-04-25 12:53 ` Juergen Gross
@ 2018-04-27 15:09 ` tip-bot for Petr Tesarik
  1 sibling, 0 replies; 3+ messages in thread
From: tip-bot for Petr Tesarik @ 2018-04-27 15:09 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: ptesarik, thomas.lendacky, boris.ostrovsky, mpatocka, tglx,
	jgross, luto, ptesarik, linux-kernel, douly.fnst, mingo,
	jdelvare, hpa, bp

Commit-ID:  3db3eb285259ac129f7aec6b814b3e9f6c1b372b
Gitweb:     https://git.kernel.org/tip/3db3eb285259ac129f7aec6b814b3e9f6c1b372b
Author:     Petr Tesarik <ptesarik@suse.cz>
AuthorDate: Wed, 25 Apr 2018 12:08:35 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 27 Apr 2018 17:06:28 +0200

x86/setup: Do not reserve a crash kernel region if booted on Xen PV

Xen PV domains cannot shut down and start a crash kernel. Instead,
the crashing kernel makes a SCHEDOP_shutdown hypercall with the
reason code SHUTDOWN_crash, cf. xen_crash_shutdown() machine op in
arch/x86/xen/enlighten_pv.c.

A crash kernel reservation is merely a waste of RAM in this case. It
may also confuse users of kexec_load(2) and/or kexec_file_load(2).
When flags include KEXEC_ON_CRASH or KEXEC_FILE_ON_CRASH,
respectively, these syscalls return success, which is technically
correct, but the crash kexec image will never be actually used.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Dou Liyang <douly.fnst@cn.fujitsu.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: xen-devel@lists.xenproject.org
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Jean Delvare <jdelvare@suse.de>
Link: https://lkml.kernel.org/r/20180425120835.23cef60c@ezekiel.suse.cz

---
 arch/x86/kernel/setup.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 6285697b6e56..5c623dfe39d1 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -50,6 +50,7 @@
 #include <linux/init_ohci1394_dma.h>
 #include <linux/kvm_para.h>
 #include <linux/dma-contiguous.h>
+#include <xen/xen.h>
 
 #include <linux/errno.h>
 #include <linux/kernel.h>
@@ -534,6 +535,11 @@ static void __init reserve_crashkernel(void)
 		high = true;
 	}
 
+	if (xen_pv_domain()) {
+		pr_info("Ignoring crashkernel for a Xen PV domain\n");
+		return;
+	}
+
 	/* 0 means: find the address automatically */
 	if (crash_base <= 0) {
 		/*

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2018-04-27 15:12 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-04-25 10:08 [PATCH] x86: Do not reserve a crash kernel region if booted on Xen PV Petr Tesarik
2018-04-25 12:53 ` Juergen Gross
2018-04-27 15:09 ` [tip:x86/urgent] x86/setup: " tip-bot for Petr Tesarik

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