Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753549AbcDKTog (ORCPT ); Mon, 11 Apr 2016 15:44:36 -0400 Received: from g4t3428.houston.hp.com ([15.201.208.56]:48088 "EHLO g4t3428.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750879AbcDKTof (ORCPT ); Mon, 11 Apr 2016 15:44:35 -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, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, Toshi Kani , David Vrabel Subject: [PATCH v2] x86/mm/pat: Fix BUG_ON in mmap_mem on QEMU/i386 Date: Mon, 11 Apr 2016 13:36:00 -0600 Message-Id: <1460403360-25441-1-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: 2736 Lines: 81 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. 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 Link: https://lkml.org/lkml/2016/4/1/608 Signed-off-by: Toshi Kani Cc: Thomas Gleixner Cc: Ingo Molnar Cc: H. Peter Anvin Cc: Borislav Petkov Cc: David Vrabel --- This patch is based on -tip. v2: Change to remove the code block. --- arch/x86/mm/pat.c | 19 ------------------- 1 file changed, 19 deletions(-) diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c index c4c3ddc..fb0604f 100644 --- a/arch/x86/mm/pat.c +++ b/arch/x86/mm/pat.c @@ -778,25 +778,6 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn, if (file->f_flags & O_DSYNC) pcm = _PAGE_CACHE_MODE_UC_MINUS; -#ifdef CONFIG_X86_32 - /* - * On the PPro and successors, the MTRRs are used to set - * memory types for physical addresses outside main memory, - * so blindly setting UC or PWT on those pages is wrong. - * For Pentiums and earlier, the surround logic should disable - * caching for the high addresses through the KEN pin, but - * we maintain the tradition of paranoia in this code. - */ - if (!pat_enabled() && - !(boot_cpu_has(X86_FEATURE_MTRR) || - 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)) { - pcm = _PAGE_CACHE_MODE_UC; - } -#endif - *vma_prot = __pgprot((pgprot_val(*vma_prot) & ~_PAGE_CACHE_MASK) | cachemode2protval(pcm)); return 1;