linux-kernel - [PATCH 26/27] KVM: x86/mmu: Add page-track API to query if a gfn is valid

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Date:   Fri, 23 Dec 2022 00:57:38 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>
Cc:     kvm@...r.kernel.org, intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Yan Zhao <yan.y.zhao@...el.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 26/27] KVM: x86/mmu: Add page-track API to query if a gfn is valid

Add a page-track API to query if a gfn is "valid", i.e. is backed by a
memslot and is visible to the guest.  This is one more step toward
removing KVM internal details from the page-track APIs.

Add a FIXME to call out that intel_gvt_is_valid_gfn() is broken with
respect to 2MiB (or larger) guest entries, e.g. if the starting gfn is
valid but a 2MiB page starting at the gfn covers "invalid" memory due
to running beyond the memslot.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/kvm_page_track.h |  1 +
 arch/x86/kvm/mmu/page_track.c         | 13 +++++++++++++
 drivers/gpu/drm/i915/gvt/gtt.c        | 11 ++---------
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index 66a0d7c34311..99e1d6eeb0fb 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -52,6 +52,7 @@ int kvm_page_track_register_notifier(struct kvm *kvm,
 void kvm_page_track_unregister_notifier(struct kvm *kvm,
 					struct kvm_page_track_notifier_node *n);
 
+bool kvm_page_track_is_valid_gfn(struct kvm *kvm, gfn_t gfn);
 int kvm_write_track_add_gfn(struct kvm *kvm, gfn_t gfn);
 int kvm_write_track_remove_gfn(struct kvm *kvm, gfn_t gfn);
 #endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 1af431a41f71..9da071a514b3 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -264,6 +264,19 @@ enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
 }
 EXPORT_SYMBOL_GPL(kvm_page_track_max_mapping_level);
 
+bool kvm_page_track_is_valid_gfn(struct kvm *kvm, gfn_t gfn)
+{
+	bool ret;
+	int idx;
+
+	idx = srcu_read_lock(&kvm->srcu);
+	ret = kvm_is_visible_gfn(kvm, gfn);
+	srcu_read_unlock(&kvm->srcu, idx);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kvm_page_track_is_valid_gfn);
+
 /*
  * add guest page to the tracking pool so that corresponding access on that
  * page will be intercepted.
diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index 59ba6639e622..43c4fc23205d 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -51,18 +51,11 @@ static int preallocated_oos_pages = 8192;
 
 static bool intel_gvt_is_valid_gfn(struct intel_vgpu *vgpu, unsigned long gfn)
 {
-	struct kvm *kvm = vgpu->vfio_device.kvm;
-	int idx;
-	bool ret;
-
 	if (!vgpu->attached)
 		return false;
 
-	idx = srcu_read_lock(&kvm->srcu);
-	ret = kvm_is_visible_gfn(kvm, gfn);
-	srcu_read_unlock(&kvm->srcu, idx);
-
-	return ret;
+	/* FIXME: This doesn't properly handle guest entries larger than 4K. */
+	return kvm_page_track_is_valid_gfn(vgpu->vfio_device.kvm, gfn);
 }
 
 /*
-- 
2.39.0.314.g84b9a713c41-goog