On Tue, Mar 21, 2023 at 3:12 PM David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > > On Tue, 2023-03-21 at 14:28 -0400, Brian Gerst wrote: > > > > > @@ -264,6 +318,14 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) > > > lgdt (%rsp) > > > addq $16, %rsp > > > > > > + /* Drop the realmode protection. For the boot CPU the pointer is NULL! */ > > > + movq trampoline_lock(%rip), %rax > > > + testq %rax, %rax > > > + jz .Lsetup_data_segments > > > + lock > > > + btrl $0, (%rax) > > > + > > > +.Lsetup_data_segments: > > > /* set up data segments */ > > > xorl %eax,%eax > > > movl %eax,%ds > > > > This can still go earlier, right after "movq TASK_threadsp(%rax), > > %rsp". The GDT descriptor is placed on the idle thread stack, so it's > > safe to drop the lock before it. > > > --- a/arch/x86/kernel/head_64.S > +++ b/arch/x86/kernel/head_64.S > @@ -335,6 +335,17 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) > movq pcpu_hot + X86_current_task(%rdx), %rax > movq TASK_threadsp(%rax), %rsp > > + /* > + * Now that this CPU is running on its own stack, drop the realmode > + * protection. For the boot CPU the pointer is NULL! > + */ > + movq trampoline_lock(%rip), %rax > + testq %rax, %rax > + jz .Lsetup_gdt > + lock > + btrl $0, (%rax) > + > +.Lsetup_gdt: > /* > * We must switch to a new descriptor in kernel space for the GDT > * because soon the kernel won't have access anymore to the userspace > @@ -377,14 +388,6 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) > shrq $32, %rdx > wrmsr > > - /* Drop the realmode protection. For the boot CPU the pointer is NULL! */ > - movq trampoline_lock(%rip), %rax > - testq %rax, %rax > - jz .Lsetup_idt > - lock > - btrl $0, (%rax) > - > -.Lsetup_idt: > /* Setup and Load IDT */ > pushq %rsi > call early_setup_idt > Looks good, thanks.
