x86/entry: Switch XEN/PV hypercall entry to IDTENTRY

Convert the XEN/PV hypercall to IDTENTRY:

  - Emit the ASM stub with DECLARE_IDTENTRY
  - Remove the ASM idtentry in 64-bit
  - Remove the open coded ASM entry code in 32-bit
  - Remove the old prototypes

The handler stubs need to stay in ASM code as they need corner case handling
and adjustment of the stack pointer.

Provide a new C function which invokes the entry/exit handling and calls
into the XEN handler on the interrupt stack if required.

The exit code is slightly different from the regular idtentry_exit() on
non-preemptible kernels. If the hypercall is preemptible and need_resched()
is set then XEN provides a preempt hypercall scheduling function.

Move this functionality into the entry code so it can use the existing
idtentry functionality.

[ mingo: Build fixes. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Juergen Gross <jgross@suse.com>
Tested-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20200521202118.055270078@linutronix.de

2 files changed, 1 insertions, 43 deletions

diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 0c4efa6fe450..0d322f3d90cd 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o
-obj-y	+= grant-table.o features.o balloon.o manage.o preempt.o time.o
+obj-y	+= grant-table.o features.o balloon.o manage.o time.o
 obj-y	+= mem-reservation.o
 obj-y	+= events/
 obj-y	+= xenbus/
diff --git a/drivers/xen/preempt.c b/drivers/xen/preempt.c
deleted file mode 100644
index 17240c5325a3..000000000000
--- a/drivers/xen/preempt.c
+++ /dev/null
@@ -1,42 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * Preemptible hypercalls
- *
- * Copyright (C) 2014 Citrix Systems R&D ltd.
- */
-
-#include <linux/sched.h>
-#include <xen/xen-ops.h>
-
-#ifndef CONFIG_PREEMPTION
-
-/*
- * Some hypercalls issued by the toolstack can take many 10s of
- * seconds. Allow tasks running hypercalls via the privcmd driver to
- * be voluntarily preempted even if full kernel preemption is
- * disabled.
- *
- * Such preemptible hypercalls are bracketed by
- * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
- * calls.
- */
-
-DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
-EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
-
-asmlinkage __visible void xen_maybe_preempt_hcall(void)
-{
-	if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
-		     && need_resched())) {
-		/*
-		 * Clear flag as we may be rescheduled on a different
-		 * cpu.
-		 */
-		__this_cpu_write(xen_in_preemptible_hcall, false);
-		local_irq_enable();
-		cond_resched();
-		local_irq_disable();
-		__this_cpu_write(xen_in_preemptible_hcall, true);
-	}
-}
-#endif /* CONFIG_PREEMPTION */