On 01/02/18 12:16, Juergen Gross wrote: > When running as Xen pv guest %gs is initialized some time after > C code is started. Depending on stack protector usage this might be > too late, resulting in page faults. > > So setup %gs and MSR_GS_BASE in assembly code already. > > Cc: sta...@vger.kernel.org > Signed-off-by: Juergen Gross <jgr...@suse.com> > --- > arch/x86/xen/xen-head.S | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S > index 497cc55a0c16..b47d87076efb 100644 > --- a/arch/x86/xen/xen-head.S > +++ b/arch/x86/xen/xen-head.S > @@ -9,7 +9,9 @@ > > #include <asm/boot.h> > #include <asm/asm.h> > +#include <asm/msr.h> > #include <asm/page_types.h> > +#include <asm/percpu.h> > #include <asm/unwind_hints.h> > > #include <xen/interface/elfnote.h> > @@ -35,6 +37,18 @@ ENTRY(startup_xen) > mov %_ASM_SI, xen_start_info > mov $init_thread_union+THREAD_SIZE, %_ASM_SP > > + /* Set up %gs. > + * > + * The base of %gs always points to the bottom of the irqstack > + * union. If the stack protector canary is enabled, it is > + * located at %gs:40. Note that, on SMP, the boot cpu uses > + * init data section till per cpu areas are set up. > + */ > + movl $MSR_GS_BASE,%ecx > + movq $INIT_PER_CPU_VAR(irq_stack_union),%rax > + cdq > + wrmsr
You surely want a #ifdef __x86_64__ ? This path is common to the 32bit entry as well? ~Andrew > + > jmp xen_start_kernel > END(startup_xen) > __FINIT
