linux-kernel - [PATCH] KVM: x86/mmu: Embed direct bits into gpa for KVM_PRE_FAULT

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Message-ID: <20250611001018.2179964-1-xiaoyao.li@intel.com>
Date: Tue, 10 Jun 2025 20:10:18 -0400
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	rick.p.edgecombe@...el.com
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yan.y.zhao@...el.com,
	reinette.chatre@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	isaku.yamahata@...el.com,
	Binbin Wu <binbin.wu@...ux.intel.com>,
	tony.lindgren@...ux.intel.com,
	xiaoyao.li@...el.com
Subject: [PATCH] KVM: x86/mmu: Embed direct bits into gpa for KVM_PRE_FAULT_MEMORY

From: Paolo Bonzini <pbonzini@...hat.com>

Bug[*] reported for TDX case when enabling KVM_PRE_FAULT_MEMORY in QEMU.

It turns out that @gpa passed to kvm_mmu_do_page_fault() doesn't have
shared bit set when the memory attribute of it is shared, and it leads
to wrong root in tdp_mmu_get_root_for_fault().

Fix it by embedding the direct bits in the gpa that is passed to
kvm_tdp_map_page(), when the memory of the gpa is not private.

[*] https://lore.kernel.org/qemu-devel/4a757796-11c2-47f1-ae0d-335626e818fd@intel.com/

Reported-by: Xiaoyao Li <xiaoyao.li@...el.com>
Closes: https://lore.kernel.org/qemu-devel/4a757796-11c2-47f1-ae0d-335626e818fd@intel.com/
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
---
we have selftests enhancement for TDX case of KVM_PRE_FAULT_MEMORY, but
the plan is to post them on top of the TDX selftests [1] when they get
upstream.

[1] https://lore.kernel.org/all/20250414214801.2693294-1-sagis@google.com/
---
 arch/x86/kvm/mmu/mmu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index cbc84c6abc2e..a4040578b537 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4896,6 +4896,7 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
 {
 	u64 error_code = PFERR_GUEST_FINAL_MASK;
 	u8 level = PG_LEVEL_4K;
+	u64 direct_bits;
 	u64 end;
 	int r;
 
@@ -4910,15 +4911,18 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
 	if (r)
 		return r;
 
+	direct_bits = 0;
 	if (kvm_arch_has_private_mem(vcpu->kvm) &&
 	    kvm_mem_is_private(vcpu->kvm, gpa_to_gfn(range->gpa)))
 		error_code |= PFERR_PRIVATE_ACCESS;
+	else
+		direct_bits = gfn_to_gpa(kvm_gfn_direct_bits(vcpu->kvm));
 
 	/*
 	 * Shadow paging uses GVA for kvm page fault, so restrict to
 	 * two-dimensional paging.
 	 */
-	r = kvm_tdp_map_page(vcpu, range->gpa, error_code, &level);
+	r = kvm_tdp_map_page(vcpu, range->gpa | direct_bits, error_code, &level);
 	if (r < 0)
 		return r;
 

base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
-- 
2.43.0