The following BUG_ON error was reported on QEMU/i386:
kernel BUG at arch/x86/mm/physaddr.c:79!
Call Trace:
phys_mem_access_prot_allowed
mmap_mem
? mmap_region
mmap_region
do_mmap
vm_mmap_pgoff
SyS_mmap_pgoff
do_int80_syscall_32
entry_INT80_32
after commit edfe63ec97ed ("x86/mtrr: Fix Xorg crashes in Qemu
sessions").
PAT is now set to disabled state when MTRRs are disabled. This
led the __pa(high_memory) check in phys_mem_access_prot_allowed()
to resurrect on x86/32.
When the system does not have much memory, 'high_memory' points to
the maximum memory address + 1, which is empty. When
CONFIG_DEBUG_VIRTUAL is also set, __pa() calls __phys_addr(), which
in turn calls slow_virt_to_phys() for high_memory. Because
high_memory does not point to a valid memory address, this address
is not mapped. Hence, BUG_ON.
Use __pa_nodebug() as the code does not expect a valid virtual
mapping for high_memory.
Reported-by: kernel test robot <ying.hu...@linux.intel.com>
Link: https://lkml.org/lkml/2016/4/1/608
Signed-off-by: Toshi Kani <toshi.k...@hpe.com>
Thomas Gleixner <t...@linutronix.de>
Ingo Molnar <mi...@kernel.org>
H. Peter Anvin <h...@zytor.com>
Borislav Petkov <b...@suse.de>
---
This patch is based on -tip.
---
arch/x86/mm/pat.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index c4c3ddc..26b7202 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -792,7 +792,7 @@ int phys_mem_access_prot_allowed(struct file *file,
unsigned long pfn,
boot_cpu_has(X86_FEATURE_K6_MTRR) ||
boot_cpu_has(X86_FEATURE_CYRIX_ARR) ||
boot_cpu_has(X86_FEATURE_CENTAUR_MCR)) &&
- (pfn << PAGE_SHIFT) >= __pa(high_memory)) {
+ (pfn << PAGE_SHIFT) >= __pa_nodebug(high_memory)) {
pcm = _PAGE_CACHE_MODE_UC;
}
#endif
