x86/xen/64, x86/entry/64: Clean up SP code in cpu_initialize_context()

I'm removing thread_struct::sp0, and Xen's usage of it is slightly
dubious and unnecessary.  Use appropriate helpers instead.

While we're at at, reorder the code slightly to make it more obvious
what's going on.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/d5b9a3da2b47c68325bd2bbe8f82d9554dee0d0f.1509609304.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 51471408fdd1329b0097f2463acff17596b83b1e..8c0e047d0b804450884b5e7964fdab6fc181a091 100644 (file)
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -13,6 +13,7 @@
  * single-threaded.
  */
 #include <linux/sched.h>
+#include <linux/sched/task_stack.h>
 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/smp.h>
@@ -293,12 +294,19 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
 #endif
        memset(&ctxt->fpu_ctxt, 0, sizeof(ctxt->fpu_ctxt));
 
+       /*
+        * Bring up the CPU in cpu_bringup_and_idle() with the stack
+        * pointing just below where pt_regs would be if it were a normal
+        * kernel entry.
+        */
        ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
        ctxt->flags = VGCF_IN_KERNEL;
        ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
        ctxt->user_regs.ds = __USER_DS;
        ctxt->user_regs.es = __USER_DS;
        ctxt->user_regs.ss = __KERNEL_DS;
+       ctxt->user_regs.cs = __KERNEL_CS;
+       ctxt->user_regs.esp = (unsigned long)task_pt_regs(idle);
 
        xen_copy_trap_info(ctxt->trap_ctxt);
 
@@ -313,8 +321,13 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
        ctxt->gdt_frames[0] = gdt_mfn;
        ctxt->gdt_ents      = GDT_ENTRIES;
 
+       /*
+        * Set SS:SP that Xen will use when entering guest kernel mode
+        * from guest user mode.  Subsequent calls to load_sp0() can
+        * change this value.
+        */
        ctxt->kernel_ss = __KERNEL_DS;
-       ctxt->kernel_sp = idle->thread.sp0;
+       ctxt->kernel_sp = task_top_of_stack(idle);
 
 #ifdef CONFIG_X86_32
        ctxt->event_callback_cs     = __KERNEL_CS;
@@ -326,10 +339,8 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
                (unsigned long)xen_hypervisor_callback;
        ctxt->failsafe_callback_eip =
                (unsigned long)xen_failsafe_callback;
-       ctxt->user_regs.cs = __KERNEL_CS;
        per_cpu(xen_cr3, cpu) = __pa(swapper_pg_dir);
 
-       ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);
        ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_gfn(swapper_pg_dir));
        if (HYPERVISOR_vcpu_op(VCPUOP_initialise, xen_vcpu_nr(cpu), ctxt))
                BUG();