Re: [PATCH v13 05/21] KVM: pfncache: remove KVM_GUEST_USES_PFN usage

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On 15/2/2024 11:29 pm, Paul Durrant wrote:
From: Paul Durrant <pdurrant@xxxxxxxxxx>

As noted in [1] the KVM_GUEST_USES_PFN usage flag is never set by any
callers of kvm_gpc_init(), which also makes the 'vcpu' argument redundant.
Moreover, all existing callers specify KVM_HOST_USES_PFN so the usage
check in hva_to_pfn_retry() and hence the 'usage' argument to
kvm_gpc_init() are also redundant.
Remove the pfn_cache_usage enumeration and remove the redundant arguments,
fields of struct gfn_to_hva_cache, and all the related code.

[1] https://lore.kernel.org/all/ZQiR8IpqOZrOpzHC@xxxxxxxxxx/

Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx

v8:
  - New in this version.
---
  arch/x86/kvm/x86.c        |  2 +-
  arch/x86/kvm/xen.c        | 14 ++++-----
  include/linux/kvm_host.h  | 11 +------
  include/linux/kvm_types.h |  8 -----
  virt/kvm/pfncache.c       | 61 ++++++---------------------------------
  5 files changed, 16 insertions(+), 80 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 16269430006f..31cd5d803dae 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12042,7 +12042,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
  	vcpu->arch.regs_avail = ~0;
  	vcpu->arch.regs_dirty = ~0;
- kvm_gpc_init(&vcpu->arch.pv_time, vcpu->kvm, vcpu, KVM_HOST_USES_PFN);
+	kvm_gpc_init(&vcpu->arch.pv_time, vcpu->kvm);
if (!irqchip_in_kernel(vcpu->kvm) || kvm_vcpu_is_reset_bsp(vcpu))
  		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 2d001a9c6378..e90464225467 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -2108,14 +2108,10 @@ void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
timer_setup(&vcpu->arch.xen.poll_timer, cancel_evtchn_poll, 0); - kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
-	kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
-	kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
-	kvm_gpc_init(&vcpu->arch.xen.vcpu_time_info_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
+	kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm);
+	kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm);
+	kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm);
+	kvm_gpc_init(&vcpu->arch.xen.vcpu_time_info_cache, vcpu->kvm);
  }
void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
@@ -2158,7 +2154,7 @@ void kvm_xen_init_vm(struct kvm *kvm)
  {
  	mutex_init(&kvm->arch.xen.xen_lock);
  	idr_init(&kvm->arch.xen.evtchn_ports);
-	kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm, NULL, KVM_HOST_USES_PFN);
+	kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm);
  }
void kvm_xen_destroy_vm(struct kvm *kvm)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5a27b4389d32..da20b7018cc8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1318,21 +1318,12 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
   *
   * @gpc:	   struct gfn_to_pfn_cache object.
   * @kvm:	   pointer to kvm instance.
- * @vcpu:	   vCPU to be used for marking pages dirty and to be woken on
- *		   invalidation.
- * @usage:	   indicates if the resulting host physical PFN is used while
- *		   the @vcpu is IN_GUEST_MODE (in which case invalidation of
- *		   the cache from MMU notifiers---but not for KVM memslot
- *		   changes!---will also force @vcpu to exit the guest and
- *		   refresh the cache); and/or if the PFN used directly
- *		   by KVM (and thus needs a kernel virtual mapping).
   *
   * This sets up a gfn_to_pfn_cache by initializing locks and assigning the
   * immutable attributes.  Note, the cache must be zero-allocated (or zeroed by
   * the caller before init).
   */
-void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
-		  struct kvm_vcpu *vcpu, enum pfn_cache_usage usage);
+void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
/**
   * kvm_gpc_activate - prepare a cached kernel mapping and HPA for a given guest
diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index 9d1f7835d8c1..d93f6522b2c3 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -49,12 +49,6 @@ typedef u64            hfn_t;
typedef hfn_t kvm_pfn_t; -enum pfn_cache_usage {
-	KVM_GUEST_USES_PFN = BIT(0),
-	KVM_HOST_USES_PFN  = BIT(1),
-	KVM_GUEST_AND_HOST_USE_PFN = KVM_GUEST_USES_PFN | KVM_HOST_USES_PFN,
-};
-
  struct gfn_to_hva_cache {
  	u64 generation;
  	gpa_t gpa;
@@ -69,13 +63,11 @@ struct gfn_to_pfn_cache {
  	unsigned long uhva;
  	struct kvm_memory_slot *memslot;
  	struct kvm *kvm;
-	struct kvm_vcpu *vcpu;
  	struct list_head list;
  	rwlock_t lock;
  	struct mutex refresh_lock;
  	void *khva;
  	kvm_pfn_t pfn;
-	enum pfn_cache_usage usage;
  	bool active;
  	bool valid;
  };
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index f3571f44d9af..6f4b537eb25b 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -25,9 +25,7 @@
  void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
  				       unsigned long end, bool may_block)
  {
-	DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS);
  	struct gfn_to_pfn_cache *gpc;
-	bool evict_vcpus = false;
spin_lock(&kvm->gpc_lock);
  	list_for_each_entry(gpc, &kvm->gpc_list, list) {
@@ -37,43 +35,10 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
  		if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
  		    gpc->uhva >= start && gpc->uhva < end) {
  			gpc->valid = false;
-
-			/*
-			 * If a guest vCPU could be using the physical address,
-			 * it needs to be forced out of guest mode.
-			 */
-			if (gpc->usage & KVM_GUEST_USES_PFN) {
-				if (!evict_vcpus) {
-					evict_vcpus = true;
-					bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS);
-				}
-				__set_bit(gpc->vcpu->vcpu_idx, vcpu_bitmap);
-			}
  		}
  		write_unlock_irq(&gpc->lock);
  	}
  	spin_unlock(&kvm->gpc_lock);
-
-	if (evict_vcpus) {
-		/*
-		 * KVM needs to ensure the vCPU is fully out of guest context
-		 * before allowing the invalidation to continue.
-		 */
-		unsigned int req = KVM_REQ_OUTSIDE_GUEST_MODE;
-		bool called;
-
-		/*
-		 * If the OOM reaper is active, then all vCPUs should have
-		 * been stopped already, so perform the request without
-		 * KVM_REQUEST_WAIT and be sad if any needed to be IPI'd.
-		 */
-		if (!may_block)
-			req &= ~KVM_REQUEST_WAIT;
-
-		called = kvm_make_vcpus_request_mask(kvm, req, vcpu_bitmap);
-
-		WARN_ON_ONCE(called && !may_block);

Starting with this change, the incoming parameter 'bool may_block' is no
longer needed. Please double check if this change is expected and if it is
worth cleaning up or leave it as it is for potential new code.

-	}
  }
bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
@@ -206,16 +171,14 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
  		 * pfn.  Note, kmap() and memremap() can both sleep, so this
  		 * too must be done outside of gpc->lock!
  		 */
-		if (gpc->usage & KVM_HOST_USES_PFN) {
-			if (new_pfn == gpc->pfn)
-				new_khva = old_khva;
-			else
-				new_khva = gpc_map(new_pfn);
-
-			if (!new_khva) {
-				kvm_release_pfn_clean(new_pfn);
-				goto out_error;
-			}
+		if (new_pfn == gpc->pfn)
+			new_khva = old_khva;
+		else
+			new_khva = gpc_map(new_pfn);
+
+		if (!new_khva) {
+			kvm_release_pfn_clean(new_pfn);
+			goto out_error;
  		}
write_lock_irq(&gpc->lock);
@@ -346,18 +309,12 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
  	return __kvm_gpc_refresh(gpc, gpc->gpa, len);
  }
-void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
-		  struct kvm_vcpu *vcpu, enum pfn_cache_usage usage)
+void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
  {
-	WARN_ON_ONCE(!usage || (usage & KVM_GUEST_AND_HOST_USE_PFN) != usage);
-	WARN_ON_ONCE((usage & KVM_GUEST_USES_PFN) && !vcpu);
-
  	rwlock_init(&gpc->lock);
  	mutex_init(&gpc->refresh_lock);
gpc->kvm = kvm;
-	gpc->vcpu = vcpu;
-	gpc->usage = usage;
  	gpc->pfn = KVM_PFN_ERR_FAULT;
  	gpc->uhva = KVM_HVA_ERR_BAD;
  }




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