linux-kernel - [PATCH 15/16] KVM: x86/tdp_mmu: Make mmu notifier callbacks to check kvm

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Date: Tue, 14 May 2024 17:59:51 -0700
From: Rick Edgecombe <rick.p.edgecombe@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	isaku.yamahata@...il.com,
	erdemaktas@...gle.com,
	sagis@...gle.com,
	yan.y.zhao@...el.com,
	dmatlack@...gle.com,
	rick.p.edgecombe@...el.com
Subject: [PATCH 15/16] KVM: x86/tdp_mmu: Make mmu notifier callbacks to check kvm_process

From: Isaku Yamahata <isaku.yamahata@...el.com>

Teach the MMU notifier callbacks how to check kvm_gfn_range.process to
filter which KVM MMU root types to operate on.

The private GPAs are backed by guest memfd. Such memory is not subjected
to MMU notifier callbacks because it can't be mapped into the host user
address space. Now kvm_gfn_range conveys info about which root to operate
on. Enhance the callback to filter the root page table type.

The KVM MMU notifier comes down to two functions.
kvm_tdp_mmu_unmap_gfn_range() and kvm_tdp_mmu_handle_gfn().

For VM's without a private/shared split in the EPT, all operations
should target the normal(shared) root. Adjust the target roots based
on kvm_gfn_shared_mask().

invalidate_range_start() comes into kvm_tdp_mmu_unmap_gfn_range().
invalidate_range_end() doesn't come into arch code.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
---
TDX MMU Part 1:
 - Remove warning (Rick)
 - Remove confusing mention of mapping flags (Chao)
 - Re-write coverletter

v19:
- type: test_gfn() => test_young()

v18:
- newly added
---
 arch/x86/kvm/mmu/tdp_mmu.c | 40 +++++++++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index eb88af48c8f0..af61d131d2dc 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1396,12 +1396,32 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	return ret;
 }
 
+static enum kvm_tdp_mmu_root_types kvm_process_to_root_types(struct kvm *kvm,
+							     enum kvm_process process)
+{
+	WARN_ON_ONCE(process == BUGGY_KVM_INVALIDATION);
+
+	/* Always process shared for cases where private is not on a separate root */
+	if (!kvm_gfn_shared_mask(kvm)) {
+		process |= KVM_PROCESS_SHARED;
+		process &= ~KVM_PROCESS_PRIVATE;
+	}
+
+	return (enum kvm_tdp_mmu_root_types)process;
+}
+
+/* Used by mmu notifier via kvm_unmap_gfn_range() */
 bool kvm_tdp_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range,
 				 bool flush)
 {
+	enum kvm_tdp_mmu_root_types types = kvm_process_to_root_types(kvm, range->process);
 	struct kvm_mmu_page *root;
 
-	__for_each_tdp_mmu_root_yield_safe(kvm, root, range->slot->as_id, KVM_ANY_ROOTS)
+	/* kvm_process_to_root_types() has WARN_ON_ONCE().  Don't warn it again. */
+	if (types == BUGGY_KVM_ROOTS)
+		return flush;
+
+	__for_each_tdp_mmu_root_yield_safe(kvm, root, range->slot->as_id, types)
 		flush = tdp_mmu_zap_leafs(kvm, root, range->start, range->end,
 					  range->may_block, flush);
 
@@ -1415,18 +1435,32 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
 						   struct kvm_gfn_range *range,
 						   tdp_handler_t handler)
 {
+	enum kvm_tdp_mmu_root_types types = kvm_process_to_root_types(kvm, range->process);
 	struct kvm_mmu_page *root;
 	struct tdp_iter iter;
 	bool ret = false;
 
+	if (types == BUGGY_KVM_ROOTS)
+		return ret;
+
 	/*
 	 * Don't support rescheduling, none of the MMU notifiers that funnel
 	 * into this helper allow blocking; it'd be dead, wasteful code.
 	 */
-	for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
+	__for_each_tdp_mmu_root(kvm, root, range->slot->as_id, types) {
+		gfn_t start, end;
+
+		/*
+		 * For TDX shared mapping, set GFN shared bit to the range,
+		 * so the handler() doesn't need to set it, to avoid duplicated
+		 * code in multiple handler()s.
+		 */
+		start = kvm_gfn_for_root(kvm, root, range->start);
+		end = kvm_gfn_for_root(kvm, root, range->end);
+
 		rcu_read_lock();
 
-		tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
+		tdp_root_for_each_leaf_pte(iter, root, start, end)
 			ret |= handler(kvm, &iter, range);
 
 		rcu_read_unlock();
-- 
2.34.1