Re: [PATCH 2/9] KVM: MMU: introduce slot_handle_level() and its helper

From: Xiao Guangrong
Date: Mon May 11 2015 - 09:04:21 EST

On 05/07/2015 08:04 PM, Paolo Bonzini wrote:

On 30/04/2015 12:24, guangrong.xiao@xxxxxxxxxxxxxxx wrote:
From: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>

There are several places walking all rmaps for the memslot so that
introduce common functions to cleanup the code

Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
arch/x86/kvm/mmu.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 63 insertions(+)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index ea3e3e4..75a3459 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4410,6 +4410,69 @@ void kvm_mmu_setup(struct kvm_vcpu *vcpu)

+/* The return value indicates if tlb flush on all vcpus is needed. */
+typedef bool (*slot_level_handler) (struct kvm *kvm, unsigned long *rmap);
+/* The caller should hold mmu-lock before calling this function. */
+static bool
+slot_handle_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
+ slot_level_handler fn, int min_level, int max_level,
+ bool lock_flush_tlb)

Why not introduce for_each_slot_rmap first, instead of introducing one
implementation first and then switching to another? It's a small
change to reorder the patches like that.

Yes, it's better, will do it in v2.

I think we should have three
iterator macros:

#define for_each_rmap_spte(rmap, iter, spte)

#define for_each_slot_rmap(slot, min_level, max_level, iter, rmapp)

#define for_each_slot_rmap_range(slot, iter, min_level, max_level, \
start_gfn, end_gfn, iter, rmapp)

where the last two take care of initializing the walker/iterator in the
first part of the "for".

Okay, i agree.

This way, this function would be introduced immediately as this very
readable code:

struct slot_rmap_iterator iter;
unsigned long *rmapp;
bool flush = false;

for_each_slot_rmap(memslot, min_level, max_level, &iter, rmapp) {
if (*rmapp)
flush |= fn(kvm, rmapp);

if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
if (flush && lock_flush_tlb) {
flush = false;

* What about adding this here: then callers that pass
* lock_flush_tlb == true need not care about the return
* value!
if (flush && lock_flush_tlb) {
flush = false;

return flush;

Good idea.

In addition, some of these functions need to be marked always_inline I
think; either slot_handle_level/slot_handle_*_level, or the
iterators/walkers. Can you collect kvm.ko size for both cases?

After applying patch 1 ~ 5:

no inline:
$ size arch/x86/kvm/kvm.ko
text data bss dec hex filename
366406 51535 473 418414 6626e arch/x86/kvm/kvm.ko

$ size arch/x86/kvm/kvm.ko
text data bss dec hex filename
366638 51535 473 418646 66356 arch/x86/kvm/kvm.ko

Since there are static functions i prefer allowing GCC automatically
optimizes the code to marking always-inline.

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