| Message ID | 1460403360-25441-1-git-send-email-toshi.kani@hpe.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* Toshi Kani <toshi.kani@hpe.com> wrote: > 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 <ying.huang@linux.intel.com> > Link: https://lkml.org/lkml/2016/4/1/608 > Signed-off-by: Toshi Kani <toshi.kani@hpe.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: H. Peter Anvin <hpa@zytor.com> > Cc: Borislav Petkov <bp@suse.de> > Cc: David Vrabel <david.vrabel@citrix.com> So you missed the Reviewed-by tag from Boris ... I've added it, but please try to propagate tags! Thanks, Ingo
On Wed, 2016-04-13 at 11:35 +0200, Ingo Molnar wrote: > * Toshi Kani <toshi.kani@hpe.com> wrote: : > > > > 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> > > Link: https://lkml.org/lkml/2016/4/1/608 > > Signed-off-by: Toshi Kani <toshi.kani@hpe.com> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: Ingo Molnar <mingo@kernel.org> > > Cc: H. Peter Anvin <hpa@zytor.com> > > Cc: Borislav Petkov <bp@suse.de> > > Cc: David Vrabel <david.vrabel@citrix.com> > > So you missed the Reviewed-by tag from Boris ... > > I've added it, but please try to propagate tags! Thanks Ingo! I decided to drop the Reviewed-by tag for v1 since v2 has a different approach. -Toshi
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;
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 <ying.huang@linux.intel.com> Link: https://lkml.org/lkml/2016/4/1/608 Signed-off-by: Toshi Kani <toshi.kani@hpe.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Borislav Petkov <bp@suse.de> Cc: David Vrabel <david.vrabel@citrix.com> --- This patch is based on -tip. v2: Change to remove the code block. --- arch/x86/mm/pat.c | 19 ------------------- 1 file changed, 19 deletions(-)