On 27/06/19 13:23, Nadav Amit wrote: > Whenever we load the GDT, we need to reload the segment selectors so > their hidden data (base, limit, type, etc.) would be reloaded. > > It appears that loading GS overwrites the GS bases, so reload GS base > after loading the segment to prevent per-cpu variable corruption. > > Signed-off-by: Nadav Amit <nadav.amit@xxxxxxxxx> > --- > x86/cstart64.S | 23 +++++++++++++++++------ > 1 file changed, 17 insertions(+), 6 deletions(-) > > diff --git a/x86/cstart64.S b/x86/cstart64.S > index c5561e7..9791282 100644 > --- a/x86/cstart64.S > +++ b/x86/cstart64.S > @@ -118,6 +118,21 @@ MSR_GS_BASE = 0xc0000101 > wrmsr > .endm > > +.macro setup_segments > + mov $MSR_GS_BASE, %ecx > + rdmsr > + > + mov $0x10, %bx > + mov %bx, %ds > + mov %bx, %es > + mov %bx, %fs > + mov %bx, %gs > + mov %bx, %ss > + > + /* restore MSR_GS_BASE */ > + wrmsr > +.endm > + > .globl start > start: > mov %ebx, mb_boot_info > @@ -149,6 +164,7 @@ switch_to_5level: > > prepare_64: > lgdt gdt64_desc > + setup_segments > > enter_long_mode: > mov %cr4, %eax > @@ -196,12 +212,7 @@ sipi_end: > > .code32 > ap_start32: > - mov $0x10, %ax > - mov %ax, %ds > - mov %ax, %es > - mov %ax, %fs > - mov %ax, %gs > - mov %ax, %ss > + setup_segments > mov $-4096, %esp > lock/xaddl %esp, smp_stacktop > setup_percpu_area > Queued, thanks. Paolo
