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

Sean Christopherson
2022-12-23T01:01:01Z

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@google.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