The following BUG_ON() crash 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:
edfe63ec97 ("x86/mtrr: Fix Xorg crashes in Qemu sessions")
PAT is now set to disabled state when MTRRs are disabled.
Thus, reactivating the __pa(high_memory) check in
phys_mem_access_prot_allowed().
When CONFIG_DEBUG_VIRTUAL is set, __pa() calls __phys_addr(),
which in turn calls slow_virt_to_phys() for 'high_memory'.
Because 'high_memory' is set to (the max direct mapped virt
addr + 1), it is not a valid virtual address. Hence,
slow_virt_to_phys() returns 0 and hit the BUG_ON. Using
__pa_nodebug() instead of __pa() will fix this BUG_ON.
However, this code block, originally written for Pentiums and
earlier, is no longer adequate since a 32-bit Xen guest has
MTRRs disabled and supports ZONE_HIGHMEM. In this setup,
this code sets UC attribute for accessing RAM in high memory
range.
Delete this code block as it has been unused for a long time.
Reported-by: kernel test robot <ying.huang@linux.intel.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1460403360-25441-1-git-send-email-toshi.kani@hpe.com
Link: https://lkml.org/lkml/2016/4/1/608
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1886297ce0