From: Scott Moser <smoser@redhat.com>
Subject: [PATCH RHEL5u2] bz245346 kexec/kdump kernel hung on Power5+ and 	Power6 based systems
Date: Tue, 30 Oct 2007 16:36:26 -0400 (EDT)
Bugzilla: 245346
Message-Id: <Pine.LNX.4.64.0710301635230.30676@squad5-lp1.lab.boston.redhat.com>
Changelog: [ppc] kexec/kdump kernel hung on Power5+ and Power6


Bug 245346 [1]
---------------

Description:
-----------
Configuring kdump and triggering a kdump on a power5+ and power6 machine
hangs the system.  This occurs on systems that have "POWER5+" or POWER6
in /proc/cpuinfo.  kdump works on systems with "POWER5".

$ echo c > /proc/sysrq-trigger
SysRq : Trigger a crashdump
Sending IPI to other cpus...  <--- it stops here

Kernel Version:
--------------
Patch built against 2.6.18-54

Upstream Status:
---------------
This change is present upstream as git commit
b7abc5c53e3c65b8e931bd96db2d08ba670e111a

Test Status:
----

I've booted the 2.6.18-54.el5.rhel5u2.sm4 kernel listed above and verified
that the dump is correctly taken on a POWER6 system where 2.6.18-53.el5
hung.  I also verified kdump works with the patched kernel on POWER5
system where it was previously working.  The "crashkernel" parameter was
set to "crashkernel=256M@16M"

$ chkconfig kdump on
$ service kdump start
$ echo c > /proc/sysrq-trigger

Then, after reboot, verified readable by crash.

Please review patch below for RHEL5u2
--
[1]:https://bugzilla.redhat.com/show_bug.cgi?id=245346
--
 arch/powerpc/platforms/pseries/lpar.c |   17 ++++++++++++++---
 include/asm-powerpc/mmu.h             |    3 +++
 2 files changed, 17 insertions(+), 3 deletions(-)
Index: b/arch/powerpc/platforms/pseries/lpar.c
===================================================================
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -377,12 +377,23 @@ static void pSeries_lpar_hptab_clear(voi
 {
 	unsigned long size_bytes = 1UL << ppc64_pft_size;
 	unsigned long hpte_count = size_bytes >> 4;
-	unsigned long dummy1, dummy2;
+	unsigned long dummy1, dummy2, dword0;
+	long lpar_rc;
 	int i;
 
 	/* TODO: Use bulk call */
-	for (i = 0; i < hpte_count; i++)
-		plpar_pte_remove(0, i, 0, &dummy1, &dummy2);
+	for (i = 0; i < hpte_count; i++) {
+		/* dont remove HPTEs with VRMA mappings */
+		lpar_rc = plpar_pte_remove(H_ANDCOND, i, HPTE_V_1TB_SEG,
+						&dummy1, &dummy2);
+		if (lpar_rc == H_NOT_FOUND) {
+			lpar_rc = plpar_pte_read(0, i, &dword0, &dummy1);
+			if (!lpar_rc && ((dword0 & HPTE_V_VRMA_MASK)
+				!= HPTE_V_VRMA_MASK))
+				/* Can be hpte for 1TB Seg. So remove it */
+				plpar_pte_remove(0, i, 0, &dummy1, &dummy2);
+		}
+	}
 }
 
 /*
Index: b/include/asm-powerpc/mmu.h
===================================================================
--- a/include/asm-powerpc/mmu.h
+++ b/include/asm-powerpc/mmu.h
@@ -100,6 +100,9 @@ extern char initial_stab[];
 #define HPTE_R_C		ASM_CONST(0x0000000000000080)
 #define HPTE_R_R		ASM_CONST(0x0000000000000100)
 
+#define HPTE_V_1TB_SEG		ASM_CONST(0x4000000000000000)
+#define HPTE_V_VRMA_MASK	ASM_CONST(0x4001ffffff000000)
+
 /* Values for PP (assumes Ks=0, Kp=1) */
 /* pp0 will always be 0 for linux     */
 #define PP_RWXX	0	/* Supervisor read/write, User none */