Messages in this thread Patch in this message | | | From | Toshi Kani <> | Subject | [PATCH] x86/mm/pat: Fix BUG_ON in mmap_mem on QEMU/i386 | Date | Fri, 1 Apr 2016 16:19:45 -0600 |
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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.huang@linux.intel.com> Link: https://lkml.org/lkml/2016/4/1/608 Signed-off-by: Toshi Kani <toshi.kani@hpe.com> Thomas Gleixner <tglx@linutronix.de> Ingo Molnar <mingo@kernel.org> H. Peter Anvin <hpa@zytor.com> Borislav Petkov <bp@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
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