KVM: Introduce kvm_follow_pfn() to eventually replace "gfn_to_pfn" APIs

Introduce kvm_follow_pfn() to eventually supplant the various "gfn_to_pfn"
APIs, albeit by adding more wrappers.  The primary motivation of the new
helper is to pass a structure instead of an ever changing set of parameters,
e.g. so that tweaking the behavior, inputs, and/or outputs of the "to pfn"
helpers doesn't require churning half of KVM.

In the more distant future, the APIs exposed to arch code could also
follow suit, e.g. by adding something akin to x86's "struct kvm_page_fault"
when faulting in guest memory.  But for now, the goal is purely to clean
up KVM's "internal" MMU code.

As part of the conversion, replace the write_fault, interruptible, and
no-wait boolean flags with FOLL_WRITE, FOLL_INTERRUPTIBLE, and FOLL_NOWAIT
respectively.  Collecting the various FOLL_* flags into a single field
will again ease the pain of passing new flags.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: David Stevens <stevensd@chromium.org>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-20-seanjc@google.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h
index 51f3fee4ca3f..d5a215958f06 100644
--- a/virt/kvm/kvm_mm.h
+++ b/virt/kvm/kvm_mm.h
@@ -20,8 +20,24 @@
 #define KVM_MMU_UNLOCK(kvm)		spin_unlock(&(kvm)->mmu_lock)
 #endif /* KVM_HAVE_MMU_RWLOCK */
 
-kvm_pfn_t hva_to_pfn(unsigned long addr, bool interruptible, bool no_wait,
-		     bool write_fault, bool *writable);
+
+struct kvm_follow_pfn {
+	const struct kvm_memory_slot *slot;
+	const gfn_t gfn;
+
+	unsigned long hva;
+
+	/* FOLL_* flags modifying lookup behavior, e.g. FOLL_WRITE. */
+	unsigned int flags;
+
+	/*
+	 * If non-NULL, try to get a writable mapping even for a read fault.
+	 * Set to true if a writable mapping was obtained.
+	 */
+	bool *map_writable;
+};
+
+kvm_pfn_t hva_to_pfn(struct kvm_follow_pfn *kfp);
 
 #ifdef CONFIG_HAVE_KVM_PFNCACHE
 void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm,