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CR4 modifications are implemented as RMW operations which update a shadow variable and write the result to CR4. The RMW operation is protected by preemption disable, but there is no enforcement or debugging mechanism. CR4 modifications happen also in interrupt context via __native_flush_tlb_global(). This implementation does not affect a interrupted thread context CR4 operation, because the CR4 toggle restores the original content and does not modify the shadow variable. So the current situation seems to be safe, but a recent patch tried to add an actual RMW operation in interrupt context, which will cause subtle corruptions. To prevent that and make the CR4 handling future proof: - Add a lockdep assertion to __cr4_set() which will catch interrupt enabled invocations - Disable interrupts in the cr4 manipulator inlines - Rename cr4_toggle_bits() to cr4_toggle_bits_irqsoff(). This is called from __switch_to_xtra() where interrupts are already disabled and performance matters. All other call sites are not performance critical, so the extra overhead of an additional local_irq_save/restore() pair is not a problem. If new call sites care about performance then the necessary _irqsoff() variants can be added. [ tglx: Condensed the patch by moving the irq protection inside the manipulator functions. Updated changelog ] Signed-off-by: Nadav Amit <namit@vmware.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Luck <tony.luck@intel.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: nadav.amit@gmail.com Cc: linux-edac@vger.kernel.org Link: https://lkml.kernel.org/r/20171125032907.2241-3-namit@vmware.com
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.