[PATCH Part2 RFC v3 25/37] KVM: X86: Introduce kvm_mmu_map_tdp_page() for use by SEV

Brijesh Singh
2021-06-02T14:15:40Z

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 7991ffae7b31..df8923fb664f 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