Re: [Xen-devel] [PATCH 1/6] xen/x86/pvh: Save %rbx in xen_pvh_early_cpu_init()

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

> > diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
> > index 8afdfcc..b1508a8 100644
> > --- a/arch/x86/xen/xen-head.S
> > +++ b/arch/x86/xen/xen-head.S
> > @@ -56,28 +56,28 @@ ENTRY(startup_xen)
> >   * @entry: true if this is a secondary vcpu coming up on this entry
> >   *         point, false if this is the boot CPU being initialized for
> >   *         the first time (%rsi)
> > - *
> > - * Note: This is called as a function on the boot CPU, and is the entry 
> > point
> > - *       on the secondary CPU.
> >   */
> >  ENTRY(xen_pvh_early_cpu_init)
> > -   mov     %rsi, %r11
> > +   mov     %rbx, -8(%rsp)

> >  
> > +/* Entry point for secondary CPUs */

Actually, could you do this (since the BSP can access the stack and
it can do jumps) - not compile tested:

This way you don't even need the second argument - as there
are two functions now - and no need to figure out whether
one is for BSP and the other for other CPUs.

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 7953e68..c8e0655 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1462,7 +1462,7 @@ static void __init xen_pvh_early_guest_init(void)
 
        xen_have_vector_callback = 1;
 
-       xen_pvh_early_cpu_init(0, false);
+       xen_pvh_early_cpu_init(0);
        xen_pvh_set_cr_flags(0);
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index ca7ee1f..e53be3b 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -426,7 +426,6 @@ cpu_initialize_context(unsigned int cpu, struct task_struct 
*idle)
                ctxt->user_regs.eip =
                        (unsigned long)xen_pvh_early_cpu_init_secondary;
                ctxt->user_regs.rdi = cpu;
-               ctxt->user_regs.rsi = true;  /* entry == true */
        }
 #endif
        ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);
diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h
index bf2b43c..bec860a 100644
--- a/arch/x86/xen/smp.h
+++ b/arch/x86/xen/smp.h
@@ -9,10 +9,10 @@ extern void xen_send_IPI_all(int vector);
 extern void xen_send_IPI_self(int vector);
 
 #ifdef CONFIG_XEN_PVH
-extern void xen_pvh_early_cpu_init(int cpu, bool entry);
+extern void xen_pvh_early_cpu_init(int cpu);
 extern void xen_pvh_early_cpu_init_secondary(int cpu, bool entry);
 #else
-static inline void xen_pvh_early_cpu_init(int cpu, bool entry)
+static inline void xen_pvh_early_cpu_init(int cpu)
 {
 }
 static inline void xen_pvh_early_cpu_init_secondary(int cpu, bool entry)
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index b1508a8..1c20669 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -53,15 +53,17 @@ ENTRY(startup_xen)
 /*
  * xen_pvh_early_cpu_init() - early PVH VCPU initialization
  * @cpu:   this cpu number (%rdi)
- * @entry: true if this is a secondary vcpu coming up on this entry
- *         point, false if this is the boot CPU being initialized for
- *         the first time (%rsi)
  */
 ENTRY(xen_pvh_early_cpu_init)
        mov     %rbx, -8(%rsp)
-
-/* Entry point for secondary CPUs */
+       xor     %esi, %esi
+       jmp     1f
+/* Entry point for secondary CPUs. Can't touch stack (no jumps!) until NX
+ * is dealt with.
+ */
 ENTRY(xen_pvh_early_cpu_init_secondary)
+       mov     $1, %esi
+1:
        /* Gather features to see if NX implemented. */
        mov     $0x80000001, %eax
        cpuid
@@ -72,9 +74,9 @@ ENTRY(xen_pvh_early_cpu_init_secondary)
        bts     $_EFER_SCE, %eax
 
        bt      $20, %ebx
-       jnc     1f              /* No NX, skip setting it */
+       jnc     2f              /* No NX, skip setting it */
        bts     $_EFER_NX, %eax
-1:     wrmsr
+2:     wrmsr
        mov     -8(%rsp), %rbx
 #ifdef CONFIG_SMP
        cmp     $0, %esi

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