KVM: Wrap kvm_{gfn,hva}_range.pte in a per-action union

Wrap kvm_{gfn,hva}_range.pte in a union so that future notifier events can
pass event specific information up and down the stack without needing to
constantly expand and churn the APIs.  Lockless aging of SPTEs will pass
around a bitmap, and support for memory attributes will pass around the
new attributes for the range.

Add a "KVM_NO_ARG" placeholder to simplify handling events without an
argument (creating a dummy union variable is midly annoying).

Opportunstically drop explicit zero-initialization of the "pte" field, as
omitting the field (now a union) has the same effect.

Cc: Yu Zhao <yuzhao@google.com>
Link: https://lore.kernel.org/all/CAOUHufagkd2Jk3_HrVoFFptRXM=hX2CV8f+M-dka-hJU4bP8kw@mail.gmail.com
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Acked-by: Yu Zhao <yuzhao@google.com>
Link: https://lore.kernel.org/r/20230729004144.1054885-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/arm64/kvm/mmu.c

@@ -1721,7 +1721,7 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 
 bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	kvm_pfn_t pfn = pte_pfn(range->pte);
+	kvm_pfn_t pfn = pte_pfn(range->arg.pte);
 
 	if (!kvm->arch.mmu.pgt)
 		return false;

arch/mips/kvm/mmu.c

@@ -447,7 +447,7 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	gpa_t gpa = range->start << PAGE_SHIFT;
-	pte_t hva_pte = range->pte;
+	pte_t hva_pte = range->arg.pte;
 	pte_t *gpa_pte = kvm_mips_pte_for_gpa(kvm, NULL, gpa);
 	pte_t old_pte;
 

arch/riscv/kvm/mmu.c

@@ -559,7 +559,7 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	int ret;
-	kvm_pfn_t pfn = pte_pfn(range->pte);
+	kvm_pfn_t pfn = pte_pfn(range->arg.pte);
 
 	if (!kvm->arch.pgd)
 		return false;

arch/x86/kvm/mmu/mmu.c

@@ -1588,7 +1588,7 @@ static __always_inline bool kvm_handle_gfn_range(struct kvm *kvm,
 	for_each_slot_rmap_range(range->slot, PG_LEVEL_4K, KVM_MAX_HUGEPAGE_LEVEL,
 				 range->start, range->end - 1, &iterator)
 		ret |= handler(kvm, iterator.rmap, range->slot, iterator.gfn,
-			       iterator.level, range->pte);
+			       iterator.level, range->arg.pte);
 
 	return ret;
 }

arch/x86/kvm/mmu/tdp_mmu.c

@@ -1241,7 +1241,7 @@ static bool set_spte_gfn(struct kvm *kvm, struct tdp_iter *iter,
 	u64 new_spte;
 
 	/* Huge pages aren't expected to be modified without first being zapped. */
-	WARN_ON(pte_huge(range->pte) || range->start + 1 != range->end);
+	WARN_ON(pte_huge(range->arg.pte) || range->start + 1 != range->end);
 
 	if (iter->level != PG_LEVEL_4K ||
 	    !is_shadow_present_pte(iter->old_spte))
@@ -1255,9 +1255,9 @@ static bool set_spte_gfn(struct kvm *kvm, struct tdp_iter *iter,
 	 */
 	tdp_mmu_iter_set_spte(kvm, iter, 0);
 
-	if (!pte_write(range->pte)) {
+	if (!pte_write(range->arg.pte)) {
 		new_spte = kvm_mmu_changed_pte_notifier_make_spte(iter->old_spte,
-								  pte_pfn(range->pte));
+								  pte_pfn(range->arg.pte));
 
 		tdp_mmu_iter_set_spte(kvm, iter, new_spte);
 	}

include/linux/kvm_host.h

@@ -256,11 +256,15 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
 #endif
 
 #ifdef KVM_ARCH_WANT_MMU_NOTIFIER
+union kvm_mmu_notifier_arg {
+	pte_t pte;
+};
+
 struct kvm_gfn_range {
 	struct kvm_memory_slot *slot;
 	gfn_t start;
 	gfn_t end;
-	pte_t pte;
+	union kvm_mmu_notifier_arg arg;
 	bool may_block;
 };
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);

virt/kvm/kvm_main.c

@@ -526,7 +526,7 @@ typedef void (*on_unlock_fn_t)(struct kvm *kvm);
 struct kvm_hva_range {
 	unsigned long start;
 	unsigned long end;
-	pte_t pte;
+	union kvm_mmu_notifier_arg arg;
 	hva_handler_t handler;
 	on_lock_fn_t on_lock;
 	on_unlock_fn_t on_unlock;
@@ -547,6 +547,8 @@ static void kvm_null_fn(void)
 }
 #define IS_KVM_NULL_FN(fn) ((fn) == (void *)kvm_null_fn)
 
+static const union kvm_mmu_notifier_arg KVM_MMU_NOTIFIER_NO_ARG;
+
 /* Iterate over each memslot intersecting [start, last] (inclusive) range */
 #define kvm_for_each_memslot_in_hva_range(node, slots, start, last)	     \
 	for (node = interval_tree_iter_first(&slots->hva_tree, start, last); \
@@ -591,7 +593,7 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 			 * bother making these conditional (to avoid writes on
 			 * the second or later invocation of the handler).
 			 */
-			gfn_range.pte = range->pte;
+			gfn_range.arg = range->arg;
 			gfn_range.may_block = range->may_block;
 
 			/*
@@ -632,14 +634,14 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
 						unsigned long start,
 						unsigned long end,
-						pte_t pte,
+						union kvm_mmu_notifier_arg arg,
 						hva_handler_t handler)
 {
 	struct kvm *kvm = mmu_notifier_to_kvm(mn);
 	const struct kvm_hva_range range = {
 		.start		= start,
 		.end		= end,
-		.pte		= pte,
+		.arg		= arg,
 		.handler	= handler,
 		.on_lock	= (void *)kvm_null_fn,
 		.on_unlock	= (void *)kvm_null_fn,
@@ -659,7 +661,6 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn
 	const struct kvm_hva_range range = {
 		.start		= start,
 		.end		= end,
-		.pte		= __pte(0),
 		.handler	= handler,
 		.on_lock	= (void *)kvm_null_fn,
 		.on_unlock	= (void *)kvm_null_fn,
@@ -693,6 +694,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
 					pte_t pte)
 {
 	struct kvm *kvm = mmu_notifier_to_kvm(mn);
+	const union kvm_mmu_notifier_arg arg = { .pte = pte };
 
 	trace_kvm_set_spte_hva(address);
 
@@ -708,7 +710,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
 	if (!READ_ONCE(kvm->mmu_invalidate_in_progress))
 		return;
 
-	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_change_spte_gfn);
+	kvm_handle_hva_range(mn, address, address + 1, arg, kvm_change_spte_gfn);
 }
 
 void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
@@ -747,7 +749,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	const struct kvm_hva_range hva_range = {
 		.start		= range->start,
 		.end		= range->end,
-		.pte		= __pte(0),
 		.handler	= kvm_unmap_gfn_range,
 		.on_lock	= kvm_mmu_invalidate_begin,
 		.on_unlock	= kvm_arch_guest_memory_reclaimed,
@@ -812,7 +813,6 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
 	const struct kvm_hva_range hva_range = {
 		.start		= range->start,
 		.end		= range->end,
-		.pte		= __pte(0),
 		.handler	= (void *)kvm_null_fn,
 		.on_lock	= kvm_mmu_invalidate_end,
 		.on_unlock	= (void *)kvm_null_fn,
@@ -845,7 +845,8 @@ static int kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn,
 {
 	trace_kvm_age_hva(start, end);
 
-	return kvm_handle_hva_range(mn, start, end, __pte(0), kvm_age_gfn);
+	return kvm_handle_hva_range(mn, start, end, KVM_MMU_NOTIFIER_NO_ARG,
+				    kvm_age_gfn);
 }
 
 static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,