Patch "x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386" has been added to the 4.4-stable tree
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This is a note to let you know that I've just added the patch titled
x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mm-pat-fix-bug_on-in-mmap_mem-on-qemu-i386.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
Quoted 1 line
From
1886297ce0c8d563a08c8a8c4c0b97743e06cd37Mon Sep 17 00:00:00 2001
From: Toshi Kani <[email protected]>
Date: Mon, 11 Apr 2016 13:36:00 -0600
Subject: x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386
From: Toshi Kani <[email protected]>
commit 1886297ce0c8d563a08c8a8c4c0b97743e06cd37 upstream.
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:
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.
--- arch/x86/mm/pat.c | 19 ------------------- 1 file changed, 19 deletions(-)
arch/x86/mm/pat.c +0 -19
@@ -777,25 +777,6 @@ int phys_mem_access_prot_allowed(structif (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 ;
Patches currently in stable-queue which might be from [email protected] are
queue-4.4/x86-mm-pat-replace-cpu_has_pat-with-boot_cpu_has.patch queue-4.4/x86-mtrr-fix-xorg-crashes-in-qemu-sessions.patch queue-4.4/x86-mm-pat-add-support-of-non-default-pat-msr-setting.patch queue-4.4/x86-xen-pat-remove-pat-table-init-code-from-xen.patch queue-4.4/x86-mtrr-fix-pat-init-handling-when-mtrr-is-disabled.patch queue-4.4/x86-mm-pat-add-pat_disable-interface.patch queue-4.4/x86-mm-pat-fix-bug_on-in-mmap_mem-on-qemu-i386.patch queue-4.4/x86-pat-document-the-pat-initialization-sequence.patch