xen: support sysenter/sysexit if hypervisor does

64-bit Xen supports sysenter for 32-bit guests, so support its
use.  (sysenter is faster than int $0x80 in 32-on-64.)

sysexit is still not supported, so we fake it up using iret.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 56 insertions, 0 deletions

diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 99223cc323be..1ac08082a4b4 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -280,6 +280,62 @@ ENTRY(xen_iret_crit_fixup)
 2:      ret
 
 
+ENTRY(xen_sysexit)
+        /* Store vcpu_info pointer for easy access.  Do it this
+           way to avoid having to reload %fs */
+#ifdef CONFIG_SMP
+        GET_THREAD_INFO(%eax)
+        movl TI_cpu(%eax),%eax
+        movl __per_cpu_offset(,%eax,4),%eax
+        mov per_cpu__xen_vcpu(%eax),%eax
+#else
+        movl per_cpu__xen_vcpu, %eax
+#endif
+
+        /* We can't actually use sysexit in a pv guest,
+           so fake it up with iret */
+        pushl $__USER_DS                /* user stack segment */
+        pushl %ecx                      /* user esp */
+        pushl PT_EFLAGS+2*4(%esp)       /* user eflags */
+        pushl $__USER_CS                /* user code segment */
+        pushl %edx                      /* user eip */
+
+xen_sysexit_start_crit:
+        /* Unmask events... */
+        movb $0, XEN_vcpu_info_mask(%eax)
+        /* ...and test for pending.
+           There's a preempt window here, but it doesn't
+           matter because we're within the critical section. */
+        testb $0xff, XEN_vcpu_info_pending(%eax)
+
+        /* If there's something pending, mask events again so we
+           can directly inject it back into the kernel. */
+        jnz   1f
+
+        movl PT_EAX+5*4(%esp),%eax
+2:      iret
+1:      movb $1, XEN_vcpu_info_mask(%eax)
+xen_sysexit_end_crit:
+        addl $5*4, %esp         /* remove iret frame */
+        /* no need to re-save regs, but need to restore kernel %fs */
+        mov $__KERNEL_PERCPU, %eax
+        mov %eax, %fs
+        jmp xen_do_upcall
+.section __ex_table,"a"
+        .align 4
+        .long 2b,iret_exc
+.previous
+
+        .globl xen_sysexit_start_crit, xen_sysexit_end_crit
+/*
+        sysexit fixup is easy, since the old frame is still sitting there
+        on the stack.  We just need to remove the new recursive
+        interrupt and return.
+ */
+ENTRY(xen_sysexit_crit_fixup)
+        addl $PT_OLDESP+5*4, %esp               /* remove frame+iret */
+        jmp xen_do_upcall
+
 /*
         Force an event check by making a hypercall,
         but preserve regs before making the call.