linux-kernel - [PATCH v18 049/121] KVM: x86/tdp_mmu: Apply mmu notifier callback to only shared GPA

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Message-Id: <9f64fe39a205b769bf08f2996efb0b5afc6c1900.1705965635.git.isaku.yamahata@intel.com>
Date: Mon, 22 Jan 2024 15:53:25 -0800
From: isaku.yamahata@...el.com
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...el.com,
	isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>,
	erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>,
	Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com,
	hang.yuan@...el.com,
	tina.zhang@...el.com
Subject: [PATCH v18 049/121] KVM: x86/tdp_mmu: Apply mmu notifier callback to only shared GPA

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

The private GPAs that typically guest memfd backs aren't subject to MMU
notifier because it isn't mapped into virtual address of user process.
kvm_tdp_mmu_handle_gfn() handles the callback of the MMU notifier,
clear_flush_young(), clear_young(), test_gfn() and change_pte().  Make
kvm_tdp_mmu_handle_gfn() aware of private mapping and skip private mapping.

Even with AS_UNMOVABLE set, those mmu notifier are called.  For example,
ksmd triggers change_pte().

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
v18:
- newly added
---
 arch/x86/kvm/mmu/tdp_mmu.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index e7514a807134..fdc6e2221c33 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1157,9 +1157,29 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
 	 * into this helper allow blocking; it'd be dead, wasteful code.
 	 */
 	for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
+		gfn_t start, end;
+
+		/*
+		 * This function is called on behalf of mmu_notifier of
+		 * clear_flush_young(), clear_young(), test_gfn(), and
+		 * change_pte().  They apply to only shared GPAs.
+		 */
+		WARN_ON_ONCE(range->only_private);
+		WARN_ON_ONCE(!range->only_shared);
+		if (is_private_sp(root))
+			continue;
+
+		/*
+		 * 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_to_shared(kvm, range->start);
+		end = kvm_gfn_to_shared(kvm, 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();
-- 
2.25.1