[PATCH v3 02/13] x86/xen: simplify flush_lazy_mmu()

arch_flush_lazy_mmu_mode() is called when outstanding batched
pgtable operations must be completed immediately. There should
however be no need to leave and re-enter lazy MMU completely. The
only part of that sequence that we really need is xen_mc_flush();
call it directly.

While at it, we can also avoid preempt_disable() if we are not
in lazy MMU mode - xen_get_lazy_mode() should tolerate preemption.

Signed-off-by: Kevin Brodsky <redacted>
---
 arch/x86/xen/mmu_pv.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 2a4a8deaf612..dcb7b0989c32 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c

@@ -2137,14 +2137,11 @@ static void xen_enter_lazy_mmu(void)
 
 static void xen_flush_lazy_mmu(void)
 {
-	preempt_disable();
-
 	if (xen_get_lazy_mode() == XEN_LAZY_MMU) {
-		arch_leave_lazy_mmu_mode();
-		arch_enter_lazy_mmu_mode();
+		preempt_disable();
+		xen_mc_flush();
+		preempt_enable();
 	}
-
-	preempt_enable();
 }
 
 static void __init xen_post_allocator_init(void)

-- 
2.47.0