From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> These patches are based on work from a team at Graz University of Technology posted here: https://github.com/IAIK/KAISER The KAISER approach keeps two copies of the page tables: one for running in the kernel and one for running userspace. But, there are a few structures that are needed for switching in and out of the kernel and a good subset of *those* are per-cpu data. Here's a short summary of the things mapped to userspace: * The gdt_page's virtual address is pointed to by the LGDT instruction. It is needed to define the segments. Deeply required by CPU to run. * cpu_tss tells the CPU, among other things, where the new stacks are after user<->kernel transitions. Needed by the CPU to make ring transitions. * exception_stacks are needed at interrupt and exception entry so that there is storage for, among other things, some temporary space to permit clobbering a register to load the kernel CR3. Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Moritz Lipp <moritz.lipp@xxxxxxxxxxxxxx> Cc: Daniel Gruss <daniel.gruss@xxxxxxxxxxxxxx> Cc: Michael Schwarz <michael.schwarz@xxxxxxxxxxxxxx> Cc: Richard Fellner <richard.fellner@xxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: x86@xxxxxxxxxx --- b/arch/x86/include/asm/desc.h | 2 +- b/arch/x86/include/asm/processor.h | 2 +- b/arch/x86/kernel/cpu/common.c | 4 ++-- b/arch/x86/kernel/process.c | 2 +- 4 files changed, 5 insertions(+), 5 deletions(-) diff -puN arch/x86/include/asm/desc.h~kaiser-prep-x86-percpu-user-mapped arch/x86/include/asm/desc.h --- a/arch/x86/include/asm/desc.h~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.913619747 -0800 +++ b/arch/x86/include/asm/desc.h 2017-11-22 15:45:45.923619747 -0800 @@ -46,7 +46,7 @@ struct gdt_page { struct desc_struct gdt[GDT_ENTRIES]; } __attribute__((aligned(PAGE_SIZE))); -DECLARE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page); +DECLARE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(struct gdt_page, gdt_page); /* Provide the original GDT */ static inline struct desc_struct *get_cpu_gdt_rw(unsigned int cpu) diff -puN arch/x86/include/asm/processor.h~kaiser-prep-x86-percpu-user-mapped arch/x86/include/asm/processor.h --- a/arch/x86/include/asm/processor.h~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.915619747 -0800 +++ b/arch/x86/include/asm/processor.h 2017-11-22 15:45:45.923619747 -0800 @@ -356,7 +356,7 @@ struct tss_struct { unsigned long io_bitmap[IO_BITMAP_LONGS + 1]; } __attribute__((__aligned__(PAGE_SIZE))); -DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss); +DECLARE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(struct tss_struct, cpu_tss); /* * sizeof(unsigned long) coming from an extra "long" at the end diff -puN arch/x86/kernel/cpu/common.c~kaiser-prep-x86-percpu-user-mapped arch/x86/kernel/cpu/common.c --- a/arch/x86/kernel/cpu/common.c~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.917619747 -0800 +++ b/arch/x86/kernel/cpu/common.c 2017-11-22 15:45:45.924619747 -0800 @@ -98,7 +98,7 @@ static const struct cpu_dev default_cpu static const struct cpu_dev *this_cpu = &default_cpu; -DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = { +DEFINE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(struct gdt_page, gdt_page) = { .gdt = { #ifdef CONFIG_X86_64 /* * We need valid kernel segments for data and code in long mode too @@ -517,7 +517,7 @@ static const unsigned int exception_stac [DEBUG_STACK - 1] = DEBUG_STKSZ }; -static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks +DEFINE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(char, exception_stacks [(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]); #endif diff -puN arch/x86/kernel/process.c~kaiser-prep-x86-percpu-user-mapped arch/x86/kernel/process.c --- a/arch/x86/kernel/process.c~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.919619747 -0800 +++ b/arch/x86/kernel/process.c 2017-11-22 15:45:45.924619747 -0800 @@ -47,7 +47,7 @@ * section. Since TSS's are completely CPU-local, we want them * on exact cacheline boundaries, to eliminate cacheline ping-pong. */ -__visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = { +__visible DEFINE_PER_CPU_SHARED_ALIGNED_USER_MAPPED(struct tss_struct, cpu_tss) = { .x86_tss = { /* * .sp0 is only used when entering ring 0 from a lower _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
