[PATCH v4 06/14] KVM: arm64: Propagate and use kvm_s2_fault_result on S2 fault

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

When stage 2 page tables fault the net result may either be that a page is
mapped, an error occurred or the fault should be retried (-EAGAIN).

When a fault succeeds it may be upgraded to a PMD size via
transparent_hugepage_adjust().

In order to support KVM pre-faulting the outcome of the fault and the
mapping size must be recorded.

Track the mapping size via new kvm_s2_fault_result struct, which is
threaded through gmem_abort(), user_mem_abort() and kvm_s2_fault_map().

PKVM and SEA aren't relevant to synthetic pre-faulting so neither
kvm_inject_sea() nor pkvm_mem_abort() are altered.

Actual hardware faulting doesn't require this information, so
kvm_handle_guest_abort() simply passes NULL kvm_s2_fault_result to
gmem_abort() and user_mem_abort().

A non-NULL result also tells the abort handlers that the caller is
pre-faulting rather than a vcpu, in which case -EAGAIN is propagated to the
caller to allow the pre-fault to be retried.

Likewise, only prepare a KVM_EXIT_MEMORY_FAULT in gmem_abort() when a real
fault is being handled, as this updates vcpu state.

No functional change intended.

Suggested-by: Vincent Donnefort <vdonnefort@google.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 arch/arm64/kvm/mmu.c | 43 +++++++++++++++++++++++++++++++------------
 1 file changed, 31 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 9d799f7c1e62..ee2a4f0faa14 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1659,6 +1659,10 @@ struct kvm_s2_fault_desc {
 	struct kvm_s2_mmu	*mmu;
 };
 
+struct kvm_s2_fault_result {
+	unsigned long mapping_size;
+};
+
 static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
 {
 	return esr_fsc_is_permission_fault(s2fd->esr);
@@ -1684,7 +1688,8 @@ static u64 kvm_s2_perm_fault_granule(const struct kvm_s2_fault_desc *s2fd)
 	return BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(level));
 }
 
-static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
+static int gmem_abort(const struct kvm_s2_fault_desc *s2fd,
+		      struct kvm_s2_fault_result *result)
 {
 	bool write_fault, exec_fault;
 	bool perm_fault = kvm_s2_fault_is_perm(s2fd);
@@ -1728,8 +1733,10 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 
 	ret = kvm_gmem_get_pfn(kvm, s2fd->memslot, gfn, &pfn, &page, NULL);
 	if (ret) {
-		kvm_prepare_memory_fault_exit(s2fd->vcpu, s2fd->fault_ipa, PAGE_SIZE,
-					      write_fault, exec_fault, false);
+		/* If result is non-NULL this is a synthetic fault. */
+		if (!result)
+			kvm_prepare_memory_fault_exit(s2fd->vcpu, s2fd->fault_ipa, PAGE_SIZE,
+						      write_fault, exec_fault, false);
 		kfree(mapping);
 		return ret;
 	}
@@ -1784,7 +1791,13 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 	if ((prot & KVM_PGTABLE_PROT_W) && !ret)
 		mark_page_dirty_in_slot(kvm, s2fd->memslot, gfn);
 
-	return ret != -EAGAIN ? ret : 0;
+	if (ret == -EAGAIN)
+		return result ? ret : 0;
+
+	if (result && !ret)
+		result->mapping_size = PAGE_SIZE;
+
+	return ret;
 }
 
 struct kvm_s2_fault_vma_info {
@@ -2108,7 +2121,8 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 			    const struct kvm_s2_fault_vma_info *s2vi,
 			    enum kvm_pgtable_prot prot,
-			    void *memcache)
+			    void *memcache,
+			    struct kvm_s2_fault_result *result)
 {
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
 	struct kvm_guest_s2_mapping *mapping = NULL;
@@ -2209,12 +2223,17 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 		mark_page_dirty_in_slot(kvm, s2fd->memslot,
 					gpa_to_gfn(canonical_ipa));
 
-	if (ret != -EAGAIN)
-		return ret;
-	return 0;
+	if (ret == -EAGAIN)
+		return result ? ret : 0;
+
+	if (result && !ret)
+		result->mapping_size = mapping_size;
+
+	return ret;
 }
 
-static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
+static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd,
+			  struct kvm_s2_fault_result *result)
 {
 	bool perm_fault = kvm_s2_fault_is_perm(s2fd);
 	struct kvm_s2_fault_vma_info s2vi = {};
@@ -2253,7 +2272,7 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
 		return ret;
 	}
 
-	return kvm_s2_fault_map(s2fd, &s2vi, prot, memcache);
+	return kvm_s2_fault_map(s2fd, &s2vi, prot, memcache, result);
 }
 
 /* Resolve the access fault by making the page young again. */
@@ -2532,9 +2551,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 				!kvm_s2_fault_is_exec(&s2fd));
 
 		if (kvm_slot_has_gmem(memslot))
-			ret = gmem_abort(&s2fd);
+			ret = gmem_abort(&s2fd, NULL);
 		else
-			ret = user_mem_abort(&s2fd);
+			ret = user_mem_abort(&s2fd, NULL);
 	}
 
 	if (ret == 0)

-- 
2.55.0