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authorMahesh Salgaonkar <mahesh@linux.vnet.ibm.com>2014-01-30 19:01:04 (GMT)
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2014-02-11 00:24:47 (GMT)
commit429d2e8342954d337abe370d957e78291032d867 (patch)
tree291d3bcb329161fd4d92faa3286cd604062c2319 /arch/powerpc
parent3ec8b78fcc5aa7745026d8d85a4e9ab52c922765 (diff)
powerpc: Fix kdump hang issue on p8 with relocation on exception enabled.
On p8 systems, with relocation on exception feature enabled we are seeing kdump kernel hang at interrupt vector 0xc*4400. The reason is, with this feature enabled, exception are raised with MMU (IR=DR=1) ON with the default offset of 0xc*4000. Since exception is raised in virtual mode it requires the vector region to be executable without which it fails to fetch and execute instruction at 0xc*4xxx. For default kernel since kernel is loaded at real 0, the htab mappings sets the entire kernel text region executable. But for relocatable kernel (e.g. kdump case) we only copy interrupt vectors down to real 0 and never marked that region as executable because in p7 and below we always get exception in real mode. This patch fixes this issue by marking htab mapping range as executable that overlaps with the interrupt vector region for relocatable kernel. Thanks to Ben who helped me to debug this issue and find the root cause. Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc')
-rw-r--r--arch/powerpc/include/asm/sections.h12
-rw-r--r--arch/powerpc/mm/hash_utils_64.c14
2 files changed, 26 insertions, 0 deletions
diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
index 4ee06fe..d0e784e 100644
--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h
@@ -8,6 +8,7 @@
#ifdef __powerpc64__
+extern char __start_interrupts[];
extern char __end_interrupts[];
extern char __prom_init_toc_start[];
@@ -21,6 +22,17 @@ static inline int in_kernel_text(unsigned long addr)
return 0;
}
+static inline int overlaps_interrupt_vector_text(unsigned long start,
+ unsigned long end)
+{
+ unsigned long real_start, real_end;
+ real_start = __start_interrupts - _stext;
+ real_end = __end_interrupts - _stext;
+
+ return start < (unsigned long)__va(real_end) &&
+ (unsigned long)__va(real_start) < end;
+}
+
static inline int overlaps_kernel_text(unsigned long start, unsigned long end)
{
return start < (unsigned long)__init_end &&
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index de68812..d766d6e 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -207,6 +207,20 @@ int htab_bolt_mapping(unsigned long vstart, unsigned long vend,
if (overlaps_kernel_text(vaddr, vaddr + step))
tprot &= ~HPTE_R_N;
+ /*
+ * If relocatable, check if it overlaps interrupt vectors that
+ * are copied down to real 0. For relocatable kernel
+ * (e.g. kdump case) we copy interrupt vectors down to real
+ * address 0. Mark that region as executable. This is
+ * because on p8 system with relocation on exception feature
+ * enabled, exceptions are raised with MMU (IR=DR=1) ON. Hence
+ * in order to execute the interrupt handlers in virtual
+ * mode the vector region need to be marked as executable.
+ */
+ if ((PHYSICAL_START > MEMORY_START) &&
+ overlaps_interrupt_vector_text(vaddr, vaddr + step))
+ tprot &= ~HPTE_R_N;
+
hash = hpt_hash(vpn, shift, ssize);
hpteg = ((hash & htab_hash_mask) * HPTES_PER_GROUP);

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