diff mbox series

[RFC,v3,12/59] KVM: x86/mmu: Zap only leaf SPTEs for deleted/moved memslot by default

Message ID 2d195882a4f834256c319aaf669ab933cbe6688a.1637799475.git.isaku.yamahata@intel.com (mailing list archive)
State New, archived
Headers show
Series KVM: X86: TDX support | expand

Commit Message

Isaku Yamahata Nov. 25, 2021, 12:19 a.m. UTC 
From: Sean Christopherson <sean.j.christopherson@intel.com>

Zap only leaf SPTEs when deleting/moving a memslot by default, and add a
module param to allow reverting to the old behavior of zapping all SPTEs
at all levels and memslots when any memslot is updated.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/kvm/mmu/mmu.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

Comments

Thomas Gleixner Nov. 25, 2021, 7:04 p.m. UTC | #1 
On Wed, Nov 24 2021 at 16:19, isaku yamahata wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Zap only leaf SPTEs when deleting/moving a memslot by default, and add a
> module param to allow reverting to the old behavior of zapping all SPTEs
> at all levels and memslots when any memslot is updated.

This changelog describes WHAT the change is doing, which can be seen in
the patch itself, but it gives zero justification neither for the change
nor for the existance of the module parameter.

Thanks,

        tglx
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 33794379949e..1e11b14f4f82 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -91,6 +91,9 @@  __MODULE_PARM_TYPE(nx_huge_pages_recovery_period_ms, "uint");
 static bool __read_mostly force_flush_and_sync_on_reuse;
 module_param_named(flush_on_reuse, force_flush_and_sync_on_reuse, bool, 0644);
 
+static bool __read_mostly memslot_update_zap_all;
+module_param(memslot_update_zap_all, bool, 0444);
+
 /*
  * When setting this variable to true it enables Two-Dimensional-Paging
  * where the hardware walks 2 page tables:
@@ -5681,11 +5684,27 @@  static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
 	return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages));
 }
 
+static void kvm_mmu_zap_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	/*
+	 * Zapping non-leaf SPTEs, a.k.a. not-last SPTEs, isn't required, worst
+	 * case scenario we'll have unused shadow pages lying around until they
+	 * are recycled due to age or when the VM is destroyed.
+	 */
+	write_lock(&kvm->mmu_lock);
+	slot_handle_level(kvm, slot, kvm_zap_rmapp, PG_LEVEL_4K,
+			  KVM_MAX_HUGEPAGE_LEVEL, true);
+	write_unlock(&kvm->mmu_lock);
+}
+
 static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm,
 			struct kvm_memory_slot *slot,
 			struct kvm_page_track_notifier_node *node)
 {
-	kvm_mmu_zap_all_fast(kvm);
+	if (memslot_update_zap_all)
+		kvm_mmu_zap_all_fast(kvm);
+	else
+		kvm_mmu_zap_memslot(kvm, slot);
 }
 
 void kvm_mmu_init_vm(struct kvm *kvm)