[PATCH Part2 RFC v2 27/37] KVM: X86: Introduce kvm_mmu_map_tdp_page() for use by SEV

[Brijesh Singh <brijesh.singh@amd.com>]

Introduce a helper to directly fault-in a TDP page without going through
the full page fault path.  This allows SEV-SNP to build the netsted page
table while handling the page state change VMGEXIT. A guest may issue a
page state change VMGEXIT before accessing the page. Create a fault so
that VMGEXIT handler can get the TDP page level and keep the TDP and RMP
page level in sync.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 arch/x86/kvm/mmu.h     |  2 ++
 arch/x86/kvm/mmu/mmu.c | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 88d0ed5225a4..005ce139c97d 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -114,6 +114,8 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu)
 int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 		       bool prefault);
 
+int kvm_mmu_map_tdp_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, int max_level);
+
 static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 					u32 err, bool prefault)
 {
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index fe2c5a704a16..d150201cf10c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3842,6 +3842,26 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 				 max_level, true);
 }
 
+int kvm_mmu_map_tdp_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, int max_level)
+{
+	int r;
+
+	/*
+	 * Loop on the page fault path to handle the case where an mmu_notifier
+	 * invalidation triggers RET_PF_RETRY.  In the normal page fault path,
+	 * KVM needs to resume the guest in case the invalidation changed any
+	 * of the page fault properties, i.e. the gpa or error code.  For this
+	 * path, the gpa and error code are fixed by the caller, and the caller
+	 * expects failure if and only if the page fault can't be fixed.
+	 */
+	do {
+		r = direct_page_fault(vcpu, gpa, error_code, false, max_level, true);
+	} while (r == RET_PF_RETRY);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(kvm_mmu_map_tdp_page);
+
 static void nonpaging_init_context(struct kvm_vcpu *vcpu,
 				   struct kvm_mmu *context)
 {
-- 
2.17.1