[PATCH 1/4] KVM: guest_memfd: add generic post_populate callback

[Nikita Kalyazin <kalyazin@amazon.com>]

This adds a generic implementation of the `post_populate` callback for
the `kvm_gmem_populate`.  The only thing it does is populates the pages
with data provided by userspace if the user pointer is not NULL,
otherwise it clears the pages.
This is supposed to be used by KVM_X86_SW_PROTECTED_VM VMs.

Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
---
 virt/kvm/guest_memfd.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 8f079a61a56d..954312fac462 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -620,6 +620,27 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
 
 #ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
+static int kvm_gmem_post_populate_generic(struct kvm *kvm, gfn_t gfn_start, kvm_pfn_t pfn,
+				  void __user *src, int order, void *opaque)
+{
+	int ret = 0, i;
+	int npages = (1 << order);
+	gfn_t gfn;
+
+	if (src) {
+		void *vaddr = kmap_local_pfn(pfn);
+
+		ret = copy_from_user(vaddr, src, npages * PAGE_SIZE);
+		if (ret)
+			ret = -EINVAL;
+		kunmap_local(vaddr);
+	} else
+		for (gfn = gfn_start, i = 0; gfn < gfn_start + npages; gfn++, i++)
+			clear_highpage(pfn_to_page(pfn + i));
+
+	return ret;
+}
+
 long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long npages,
 		       kvm_gmem_populate_cb post_populate, void *opaque)
 {
-- 
2.40.1