Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754812AbcDAW2L (ORCPT ); Fri, 1 Apr 2016 18:28:11 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:59329 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752473AbcDAW2J (ORCPT ); Fri, 1 Apr 2016 18:28:09 -0400 From: Toshi Kani To: mingo@kernel.org, bp@suse.de, hpa@zytor.com, tglx@linutronix.de Cc: ying.huang@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, 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 Message-Id: <1459549185-14911-1-git-send-email-toshi.kani@hpe.com> X-Mailer: git-send-email 2.5.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1837 Lines: 57 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 Link: https://lkml.org/lkml/2016/4/1/608 Signed-off-by: Toshi Kani Thomas Gleixner Ingo Molnar H. Peter Anvin Borislav Petkov --- 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