ANDROID: KVM: arm64: Add hyp_memcache helpers for pkvm

Introduce helper functions easing the manipulation of a hyp_memcache at
EL2 in nVHE protected mode.

Signed-off-by: Quentin Perret <qperret@google.com>
Bug: 209580772
Change-Id: I3c1bda86eae67adfa4d0424e68aa5e842562b43c
Signed-off-by: Will Deacon <willdeacon@google.com>

arch/arm64/kvm/hyp/include/nvhe/mem_protect.h

@@ -67,6 +67,8 @@ void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt);
 
 int hyp_pin_shared_mem(void *from, void *to);
 void hyp_unpin_shared_mem(void *from, void *to);
+int refill_memcache(struct kvm_hyp_memcache *mc, unsigned long min_pages,
+		    struct kvm_hyp_memcache *host_mc);
 
 static __always_inline void __load_host_stage2(void)
 {

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

@@ -14,6 +14,7 @@
 #include <nvhe/early_alloc.h>
 #include <nvhe/gfp.h>
 #include <nvhe/memory.h>
+#include <nvhe/mem_protect.h>
 #include <nvhe/mm.h>
 #include <nvhe/spinlock.h>
 
@@ -210,3 +211,30 @@ int hyp_create_idmap(u32 hyp_va_bits)
 
 	return __pkvm_create_mappings(start, end - start, start, PAGE_HYP_EXEC);
 }
+
+static void *admit_host_page(void *arg)
+{
+	struct kvm_hyp_memcache *host_mc = arg;
+
+	if (!host_mc->nr_pages)
+		return NULL;
+
+	/*
+	 * The host still owns the pages in its memcache, so we need to go
+	 * through a full host-to-hyp donation cycle to change it. Fortunately,
+	 * __pkvm_host_donate_hyp() takes care of races for us, so if it
+	 * succeeds we're good to go.
+	 */
+	if (__pkvm_host_donate_hyp(hyp_phys_to_pfn(host_mc->head), 1))
+		return NULL;
+
+	return pop_hyp_memcache(host_mc, hyp_phys_to_virt);
+}
+
+/* Refill our local memcache by poping pages from the one provided by the host. */
+int refill_memcache(struct kvm_hyp_memcache *mc, unsigned long min_pages,
+		    struct kvm_hyp_memcache *host_mc)
+{
+	return __topup_hyp_memcache(mc, min_pages, admit_host_page,
+				    hyp_virt_to_phys, host_mc);
+}