Commit 928a4c39 authored Feb 10, 2018 by David Woodhouse Committed by Ingo Molnar Feb 13, 2018

KVM/x86: Reduce retpoline performance impact in slot_handle_level_range(), by...


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

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.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: Filippo Sironi <sironi@amazon.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Filippo Sironi <sironi@amazon.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arjan.van.de.ven@intel.com
Cc: dave.hansen@intel.com
Cc: jmattson@google.com
Cc: karahmed@amazon.de
Cc: kvm@vger.kernel.org
Cc: rkrcmar@redhat.com
Link: http://lkml.kernel.org/r/1518305967-31356-4-git-send-email-dwmw@amazon.co.uk


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent f208820a

arch/x86/kvm/mmu.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -5058,7 +5058,7 @@ 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)
		@@ -5088,7 +5088,7 @@ slot_handle_level_range(struct kvm kvm, struct kvm_memory_slot memslot,
		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)
		@@ -5099,7 +5099,7 @@ slot_handle_level(struct kvm kvm, struct kvm_memory_slot memslot,
		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)
		{
		@@ -5107,7 +5107,7 @@ slot_handle_all_level(struct kvm kvm, struct kvm_memory_slot memslot,
		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)
		{
		@@ -5115,7 +5115,7 @@ slot_handle_large_level(struct kvm kvm, struct kvm_memory_slot memslot,
		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)
		{

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