Patch "KVM/x86: Reduce retpoline performance impact in slot_handle_level_range(), by always inlining iterator helper methods" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

KVM/x86: Reduce retpoline performance impact in slot_handle_level_range(), by always inlining iterator helper methods

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-reduce-retpoline-performance-impact-in-slot_handle_level_range-by-always-inlining-iterator-helper-methods.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Woodhouse <[email protected]>
Date: Sat, 10 Feb 2018 23:39:24 +0000
Subject: KVM/x86: Reduce retpoline performance impact in slot_handle_level_range(), by always inlining iterator helper methods
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From: David Woodhouse <[email protected]>

commit 928a4c39484281f8ca366f53a1db79330d058401 upstream.

With retpoline, tight loops of "call this function for every XXX" are very much pessimised by taking a prediction miss *every* time. This one is by far the biggest contributor to the guest launch time with retpoline.

By marking the iterator slot_handle_…() functions always_inline, we can ensure that the indirect function call can be optimised away into a direct call and it actually generates slightly smaller code because some of the other conditionals can get optimised away too.

Performance is now pretty close to what we see with nospectre_v2 on the command line.

---
 arch/x86/kvm/mmu.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

@@ -5063,7 +5063,7 @@ void kvm_mmu_uninit_vm(struct kvm *kvm)
 typedef bool (*slot_level_handler) (struct kvm *kvm, struct kvm_rmap_head *rmap_head);
 
 /* The caller should hold mmu-lock before calling this function. */
-static bool
+static __always_inline bool
 slot_handle_level_range(struct kvm *kvm, struct kvm_memory_slot *memslot,
 			slot_level_handler fn, int start_level, int end_level,
 			gfn_t start_gfn, gfn_t end_gfn, bool lock_flush_tlb)

@@ -5093,7 +5093,7 @@ slot_handle_level_range(struct kvm *kvm,
 	return flush;
 }
 
-static bool
+static __always_inline bool
 slot_handle_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
 		  slot_level_handler fn, int start_level, int end_level,
 		  bool lock_flush_tlb)

@@ -5104,7 +5104,7 @@ slot_handle_level(struct kvm *kvm, struc
 			lock_flush_tlb);
 }
 
-static bool
+static __always_inline bool
 slot_handle_all_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
 		      slot_level_handler fn, bool lock_flush_tlb)
 {

@@ -5112,7 +5112,7 @@ slot_handle_all_level(struct kvm *kvm, s
 				 PT_MAX_HUGEPAGE_LEVEL, lock_flush_tlb);
 }
 
-static bool
+static __always_inline bool
 slot_handle_large_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
 			slot_level_handler fn, bool lock_flush_tlb)
 {

@@ -5120,7 +5120,7 @@ slot_handle_large_level(struct kvm *kvm,
 				 PT_MAX_HUGEPAGE_LEVEL, lock_flush_tlb);
 }
 
-static bool
+static __always_inline bool
 slot_handle_leaf(struct kvm *kvm, struct kvm_memory_slot *memslot,
 		 slot_level_handler fn, bool lock_flush_tlb)
 {

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/kvm-nvmx-set-the-cpu_based_use_msr_bitmaps-if-we-have-a-valid-l02-msr-bitmap.patch queue-4.14/x86-nvmx-properly-set-spec_ctrl-and-pred_cmd-before-merging-msrs.patch queue-4.14/x86-speculation-update-speculation-control-microcode-blacklist.patch queue-4.14/x86-speculation-correct-speculation-control-microcode-blacklist-again.patch queue-4.14/kvm-x86-reduce-retpoline-performance-impact-in-slot_handle_level_range-by-always-inlining-iterator-helper-methods.patch queue-4.14/x86-speculation-clean-up-various-spectre-related-details.patch queue-4.14/revert-x86-speculation-simplify-indirect_branch_prediction_barrier.patch