x86_64 - Fix FS/GS registers for VT execution
PATCH 1/1 x86_64 - Fix FS/GS registers for VT execution
Hi Andi, as we discussed, FS/GS segment state doesn't allow VT execution during boot. Patch fixes this problem. Please apply. I will be sending for -stable review when upstream.
Thanks,
Zach
Initialize FS and GS to __KERNEL_DS as well. The actual value of them is not important, but it is important to reload them in protected mode. At this time, they still retain the real mode values from initial boot. VT disallows execution of code under such conditions, which means hardware virtualization can not be used to boot the kernel on Intel platforms, making the boot time painfully slow.
This requires moving the GS load before the load of GS_BASE, so just move all the segments loads there to keep them together in the code.
arch/x86_64/kernel/head.S +14 -6
@@ -163,6 +163,20 @@ startup_64: */ lgdt cpu_gdt_descr + /* set up data segments. actually 0 would do too */ + movl $__KERNEL_DS,%eax + movl %eax,%ds + movl %eax,%ss + movl %eax,%es + + /* + * We don't really need to load %fs or %gs, but load them anyway + * to kill any stale realmode selectors. This allows execution + * under VT hardware. + */ + movl %eax,%fs + movl %eax,%gs + /* * Setup up a dummy PDA. this is just for some early bootup code * that does in_interrupt()
@@ -173,12 +187,6 @@ startup_64: shrq $32,%rdx wrmsr - /* set up data segments. actually 0 would do too */ - movl $__KERNEL_DS,%eax - movl %eax,%ds - movl %eax,%ss - movl %eax,%es - /* esi is pointer to real mode structure with interesting info. pass it to C */ movl %esi, %edi