KVM: arm64: Implement __pkvm_host_share_hyp() using do_share()

__pkvm_host_share_hyp() shares memory between the host and the
hypervisor so implement it as an invocation of the new do_share()
mechanism.

Note that double-sharing is no longer permitted (as this allows us to
reduce the number of page-table walks significantly), but is thankfully
no longer relied upon by the host.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211215161232.1480836-12-qperret@google.com

arch/arm64/kvm/hyp/nvhe/mem_protect.c

@@ -370,94 +370,6 @@ static int host_stage2_idmap(u64 addr)
 	return ret;
 }
 
-static inline bool check_prot(enum kvm_pgtable_prot prot,
-			      enum kvm_pgtable_prot required,
-			      enum kvm_pgtable_prot denied)
-{
-	return (prot & (required | denied)) == required;
-}
-
-int __pkvm_host_share_hyp(u64 pfn)
-{
-	phys_addr_t addr = hyp_pfn_to_phys(pfn);
-	enum kvm_pgtable_prot prot, cur;
-	void *virt = __hyp_va(addr);
-	enum pkvm_page_state state;
-	kvm_pte_t pte;
-	int ret;
-
-	if (!addr_is_memory(addr))
-		return -EINVAL;
-
-	host_lock_component();
-	hyp_lock_component();
-
-	ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, NULL);
-	if (ret)
-		goto unlock;
-	if (!pte)
-		goto map_shared;
-
-	/*
-	 * Check attributes in the host stage-2 PTE. We need the page to be:
-	 *  - mapped RWX as we're sharing memory;
-	 *  - not borrowed, as that implies absence of ownership.
-	 * Otherwise, we can't let it got through
-	 */
-	cur = kvm_pgtable_stage2_pte_prot(pte);
-	prot = pkvm_mkstate(0, PKVM_PAGE_SHARED_BORROWED);
-	if (!check_prot(cur, PKVM_HOST_MEM_PROT, prot)) {
-		ret = -EPERM;
-		goto unlock;
-	}
-
-	state = pkvm_getstate(cur);
-	if (state == PKVM_PAGE_OWNED)
-		goto map_shared;
-
-	/*
-	 * Tolerate double-sharing the same page, but this requires
-	 * cross-checking the hypervisor stage-1.
-	 */
-	if (state != PKVM_PAGE_SHARED_OWNED) {
-		ret = -EPERM;
-		goto unlock;
-	}
-
-	ret = kvm_pgtable_get_leaf(&pkvm_pgtable, (u64)virt, &pte, NULL);
-	if (ret)
-		goto unlock;
-
-	/*
-	 * If the page has been shared with the hypervisor, it must be
-	 * already mapped as SHARED_BORROWED in its stage-1.
-	 */
-	cur = kvm_pgtable_hyp_pte_prot(pte);
-	prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED);
-	if (!check_prot(cur, prot, ~prot))
-		ret = -EPERM;
-	goto unlock;
-
-map_shared:
-	/*
-	 * If the page is not yet shared, adjust mappings in both page-tables
-	 * while both locks are held.
-	 */
-	prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED);
-	ret = pkvm_create_mappings_locked(virt, virt + PAGE_SIZE, prot);
-	BUG_ON(ret);
-
-	prot = pkvm_mkstate(PKVM_HOST_MEM_PROT, PKVM_PAGE_SHARED_OWNED);
-	ret = host_stage2_idmap_locked(addr, PAGE_SIZE, prot);
-	BUG_ON(ret);
-
-unlock:
-	hyp_unlock_component();
-	host_unlock_component();
-
-	return ret;
-}
-
 void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 {
 	struct kvm_vcpu_fault_info fault;
@@ -708,3 +620,36 @@ static int do_share(struct pkvm_mem_share *share)
 
 	return WARN_ON(__do_share(share));
 }
+
+int __pkvm_host_share_hyp(u64 pfn)
+{
+	int ret;
+	u64 host_addr = hyp_pfn_to_phys(pfn);
+	u64 hyp_addr = (u64)__hyp_va(host_addr);
+	struct pkvm_mem_share share = {
+		.tx	= {
+			.nr_pages	= 1,
+			.initiator	= {
+				.id	= PKVM_ID_HOST,
+				.addr	= host_addr,
+				.host	= {
+					.completer_addr = hyp_addr,
+				},
+			},
+			.completer	= {
+				.id	= PKVM_ID_HYP,
+			},
+		},
+		.completer_prot	= PAGE_HYP,
+	};
+
+	host_lock_component();
+	hyp_lock_component();
+
+	ret = do_share(&share);
+
+	hyp_unlock_component();
+	host_unlock_component();
+
+	return ret;
+}