Commit 601f8af0 authored by David Matlack's avatar David Matlack Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Leverage vcpu->last_used_slot for rmap_add and rmap_recycle 



rmap_add() and rmap_recycle() both run in the context of the vCPU and
thus we can use kvm_vcpu_gfn_to_memslot() to look up the memslot. This
enables rmap_add() and rmap_recycle() to take advantage of
vcpu->last_used_slot and avoid expensive memslot searching.

This change improves the performance of "Populate memory time" in
dirty_log_perf_test with tdp_mmu=N. In addition to improving the
performance, "Populate memory time" no longer scales with the number
of memslots in the VM.

Command                         | Before           | After
------------------------------- | ---------------- | -------------
./dirty_log_perf_test -v64 -x1  | 15.18001570s     | 14.99469366s
./dirty_log_perf_test -v64 -x64 | 18.71336392s     | 14.98675076s

Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarDavid Matlack <dmatlack@google.com>
Message-Id: <20210804222844.1419481-6-dmatlack@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 081de470

arch/x86/kvm/mmu/mmu.c

+20 −15
Original line number Diff line number Diff line
@@ -1044,17 +1044,6 @@ static struct kvm_rmap_head *__gfn_to_rmap(gfn_t gfn, int level, 
	return &slot->arch.rmap[level - PG_LEVEL_4K][idx];

}



static struct kvm_rmap_head *gfn_to_rmap(struct kvm *kvm, gfn_t gfn,

					 struct kvm_mmu_page *sp)

{

	struct kvm_memslots *slots;

	struct kvm_memory_slot *slot;



	slots = kvm_memslots_for_spte_role(kvm, sp->role);

	slot = __gfn_to_memslot(slots, gfn);

	return __gfn_to_rmap(gfn, sp->role.level, slot);

}



static bool rmap_can_add(struct kvm_vcpu *vcpu)

{

	struct kvm_mmu_memory_cache *mc;
@@ -1065,24 +1054,39 @@ static bool rmap_can_add(struct kvm_vcpu *vcpu) 


static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)

{

	struct kvm_memory_slot *slot;

	struct kvm_mmu_page *sp;

	struct kvm_rmap_head *rmap_head;



	sp = sptep_to_sp(spte);

	kvm_mmu_page_set_gfn(sp, spte - sp->spt, gfn);

	rmap_head = gfn_to_rmap(vcpu->kvm, gfn, sp);

	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);

	rmap_head = __gfn_to_rmap(gfn, sp->role.level, slot);

	return pte_list_add(vcpu, spte, rmap_head);

}





static void rmap_remove(struct kvm *kvm, u64 *spte)

{

	struct kvm_memslots *slots;

	struct kvm_memory_slot *slot;

	struct kvm_mmu_page *sp;

	gfn_t gfn;

	struct kvm_rmap_head *rmap_head;



	sp = sptep_to_sp(spte);

	gfn = kvm_mmu_page_get_gfn(sp, spte - sp->spt);

	rmap_head = gfn_to_rmap(kvm, gfn, sp);



	/*

	 * Unlike rmap_add and rmap_recycle, rmap_remove does not run in the

	 * context of a vCPU so have to determine which memslots to use based

	 * on context information in sp->role.

	 */

	slots = kvm_memslots_for_spte_role(kvm, sp->role);



	slot = __gfn_to_memslot(slots, gfn);

	rmap_head = __gfn_to_rmap(gfn, sp->role.level, slot);



	__pte_list_remove(spte, rmap_head);

}
@@ -1620,12 +1624,13 @@ static bool kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head, 


static void rmap_recycle(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)

{

	struct kvm_memory_slot *slot;

	struct kvm_rmap_head *rmap_head;

	struct kvm_mmu_page *sp;



	sp = sptep_to_sp(spte);



	rmap_head = gfn_to_rmap(vcpu->kvm, gfn, sp);

	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);

	rmap_head = __gfn_to_rmap(gfn, sp->role.level, slot);



	kvm_unmap_rmapp(vcpu->kvm, rmap_head, NULL, gfn, sp->role.level, __pte(0));

	kvm_flush_remote_tlbs_with_address(vcpu->kvm, sp->gfn,