3.16.57-rc1 review patch. If anyone has any objections, please let me know.
------------------ From: Juergen Gross <[email protected]> commit 4f277295e54c5b7340e48efea3fc5cc21a2872b7 upstream. 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. Signed-off-by: Juergen Gross <[email protected]> Reviewed-by: Boris Ostrovsky <[email protected]> Tested-by: Chris Patterson <[email protected]> Signed-off-by: Juergen Gross <[email protected]> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <[email protected]> --- --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -8,7 +8,9 @@ #include <asm/boot.h> #include <asm/asm.h> +#include <asm/msr.h> #include <asm/page_types.h> +#include <asm/percpu.h> #include <xen/interface/elfnote.h> #include <xen/interface/features.h> @@ -42,7 +44,20 @@ ENTRY(startup_xen) #else mov %rsi,xen_start_info mov $init_thread_union+THREAD_SIZE,%rsp + + /* 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 #endif + jmp xen_start_kernel __FINIT
