[ 3.5.y.z extended stable ] Patch "xen/mmu: Use Xen specific TLB flush instead of the generic" has been added to staging queue

[Herton Ronaldo Krzesinski]

This is a note to let you know that I have just added a patch titled

    xen/mmu: Use Xen specific TLB flush instead of the generic

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From c02fa7a1de406dc520aef58e475ce89bccfe8bac Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Date: Wed, 31 Oct 2012 12:38:31 -0400
Subject: [PATCH] xen/mmu: Use Xen specific TLB flush instead of the generic
 one.
X-Extended-Stable: 3.5

commit 95a7d76897c1e7243d4137037c66d15cbf2cce76 upstream.

As Mukesh explained it, the MMUEXT_TLB_FLUSH_ALL allows the
hypervisor to do a TLB flush on all active vCPUs. If instead
we were using the generic one (which ends up being xen_flush_tlb)
we end up making the MMUEXT_TLB_FLUSH_LOCAL hypercall. But
before we make that hypercall the kernel will IPI all of the
vCPUs (even those that were asleep from the hypervisor
perspective). The end result is that we needlessly wake them
up and do a TLB flush when we can just let the hypervisor
do it correctly.

This patch gives around 50% speed improvement when migrating
idle guest's from one host to another.

Oracle-bug: 14630170

Tested-by:  Jingjie Jiang <jingjie.jiang at oracle.com>
Suggested-by:  Mukesh Rathor <mukesh.rathor at oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 arch/x86/xen/mmu.c         |   21 ++++++++++++++++++++-
 include/trace/events/xen.h |    8 ++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 3a73785..dc5c3e3 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1203,6 +1203,25 @@ unsigned long xen_read_cr2_direct(void)
 	return this_cpu_read(xen_vcpu_info.arch.cr2);
 }

+void xen_flush_tlb_all(void)
+{
+	struct mmuext_op *op;
+	struct multicall_space mcs;
+
+	trace_xen_mmu_flush_tlb_all(0);
+
+	preempt_disable();
+
+	mcs = xen_mc_entry(sizeof(*op));
+
+	op = mcs.args;
+	op->cmd = MMUEXT_TLB_FLUSH_ALL;
+	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
+
+	xen_mc_issue(PARAVIRT_LAZY_MMU);
+
+	preempt_enable();
+}
 static void xen_flush_tlb(void)
 {
 	struct mmuext_op *op;
@@ -2339,7 +2358,7 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
 	err = 0;
 out:

-	flush_tlb_all();
+	xen_flush_tlb_all();

 	return err;
 }
diff --git a/include/trace/events/xen.h b/include/trace/events/xen.h
index 92f1a79..348c4fe 100644
--- a/include/trace/events/xen.h
+++ b/include/trace/events/xen.h
@@ -377,6 +377,14 @@ DECLARE_EVENT_CLASS(xen_mmu_pgd,
 DEFINE_XEN_MMU_PGD_EVENT(xen_mmu_pgd_pin);
 DEFINE_XEN_MMU_PGD_EVENT(xen_mmu_pgd_unpin);

+TRACE_EVENT(xen_mmu_flush_tlb_all,
+	    TP_PROTO(int x),
+	    TP_ARGS(x),
+	    TP_STRUCT__entry(__array(char, x, 0)),
+	    TP_fast_assign((void)x),
+	    TP_printk("%s", "")
+	);
+
 TRACE_EVENT(xen_mmu_flush_tlb,
 	    TP_PROTO(int x),
 	    TP_ARGS(x),
--
1.7.9.5