linux-kernel - [PATCH] x86: Do not reserve a crash kernel region if booted on Xen PV

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Date:   Wed, 25 Apr 2018 12:08:35 +0200
From:   Petr Tesarik <ptesarik@...e.cz>
To:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...e.de>, Juergen Gross <jgross@...e.com>,
        Andy Lutomirski <luto@...nel.org>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Jean Delvare <jdelvare@...e.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dou Liyang <douly.fnst@...fujitsu.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86: 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@...e.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