Commit-ID: 929bacec21478a72c78e4f29f98fb799bd00105a Gitweb: https://git.kernel.org/tip/929bacec21478a72c78e4f29f98fb799bd00105a Author: Andy Lutomirski <l...@kernel.org> AuthorDate: Thu, 2 Nov 2017 00:59:08 -0700 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 2 Nov 2017 11:04:42 +0100
x86/entry/64: De-Xen-ify our NMI code Xen PV is fundamentally incompatible with our fancy NMI code: it doesn't use IST at all, and Xen entries clobber two stack slots below the hardware frame. Drop Xen PV support from our NMI code entirely. Signed-off-by: Andy Lutomirski <l...@kernel.org> Reviewed-by: Borislav Petkov <b...@suse.de> Acked-by: Juergen Gross <jgr...@suse.com> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com> Cc: Borislav Petkov <bpet...@suse.de> Cc: Brian Gerst <brge...@gmail.com> Cc: Dave Hansen <dave.han...@intel.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/bfbe711b5ae03f672f8848999a8eb2711efc7f98.1509609304.git.l...@kernel.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/entry/entry_64.S | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index a3f76ab..40e9933 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1240,9 +1240,13 @@ ENTRY(error_exit) jmp retint_user END(error_exit) -/* Runs on exception stack */ +/* + * Runs on exception stack. Xen PV does not go through this path at all, + * so we can use real assembly here. + */ ENTRY(nmi) UNWIND_HINT_IRET_REGS + /* * We allow breakpoints in NMIs. If a breakpoint occurs, then * the iretq it performs will take us out of NMI context. @@ -1300,7 +1304,7 @@ ENTRY(nmi) * stacks lest we corrupt the "NMI executing" variable. */ - SWAPGS_UNSAFE_STACK + swapgs cld movq %rsp, %rdx movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp @@ -1465,7 +1469,7 @@ nested_nmi_out: popq %rdx /* We are returning to kernel mode, so this cannot result in a fault. */ - INTERRUPT_RETURN + iretq first_nmi: /* Restore rdx. */ @@ -1496,7 +1500,7 @@ first_nmi: pushfq /* RFLAGS */ pushq $__KERNEL_CS /* CS */ pushq $1f /* RIP */ - INTERRUPT_RETURN /* continues at repeat_nmi below */ + iretq /* continues at repeat_nmi below */ UNWIND_HINT_IRET_REGS 1: #endif @@ -1571,20 +1575,22 @@ nmi_restore: /* * Clear "NMI executing". Set DF first so that we can easily * distinguish the remaining code between here and IRET from - * the SYSCALL entry and exit paths. On a native kernel, we - * could just inspect RIP, but, on paravirt kernels, - * INTERRUPT_RETURN can translate into a jump into a - * hypercall page. + * the SYSCALL entry and exit paths. + * + * We arguably should just inspect RIP instead, but I (Andy) wrote + * this code when I had the misapprehension that Xen PV supported + * NMIs, and Xen PV would break that approach. */ std movq $0, 5*8(%rsp) /* clear "NMI executing" */ /* - * INTERRUPT_RETURN reads the "iret" frame and exits the NMI - * stack in a single instruction. We are returning to kernel - * mode, so this cannot result in a fault. + * iretq reads the "iret" frame and exits the NMI stack in a + * single instruction. We are returning to kernel mode, so this + * cannot result in a fault. Similarly, we don't need to worry + * about espfix64 on the way back to kernel mode. */ - INTERRUPT_RETURN + iretq END(nmi) ENTRY(ignore_sysret)
