KVM: x86/mmu: Embed direct bits into gpa for KVM_PRE_FAULT_MEMORY

JIRA: https://issues.redhat.com/browse/RHEL-47242

commit aa2024c
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Tue Jun 10 20:10:18 2025 -0400

    KVM: x86/mmu: Embed direct bits into gpa for KVM_PRE_FAULT_MEMORY

    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@intel.com>
    Closes: https://lore.kernel.org/qemu-devel/4a757796-11c2-47f1-ae0d-335626e818fd@intel.com/
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
    Message-ID: <20250611001018.2179964-1-xiaoyao.li@intel.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>

Author: Maxim Levitsky

arch/x86/kvm/mmu/mmu.c

@@ -4895,6 +4895,7 @@ 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;
 
@@ -4909,15 +4910,18 @@ 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;