[RFC 11/16] KVM: Rework copy_to/from_guest() to avoid direct mapping

Kirill A. Shutemov
2020-05-22T12:53:34Z

We are going unmap guest pages from direct mapping and cannot rely on it
for guest memory access. Use temporary kmap_atomic()-style mapping to
access guest memory.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
virt/kvm/kvm_main.c | 57 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 55 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 07d45da5d2aa..63282def3760 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2258,17 +2258,45 @@ static int next_segment(unsigned long len, int offset)
return len;
}

+static pte_t **guest_map_ptes;
+static struct vm_struct *guest_map_area;
+
+static void *map_page_atomic(struct page *page)
+{
+ pte_t *pte;
+ void *vaddr;
+
+ preempt_disable();
+ pte = guest_map_ptes[smp_processor_id()];
+ vaddr = guest_map_area->addr + smp_processor_id() * PAGE_SIZE;
+ set_pte(pte, mk_pte(page, PAGE_KERNEL));
+ return vaddr;
+}
+
+static void unmap_page_atomic(void *vaddr)
+{
+ pte_t *pte = guest_map_ptes[smp_processor_id()];
+ set_pte(pte, __pte(0));
+ __flush_tlb_one_kernel((unsigned long)vaddr);
+ preempt_enable();
+}
+
int copy_from_guest(void *data, unsigned long hva, int len)
{
int offset = offset_in_page(hva);
struct page *page;
int npages, seg;
+ void *vaddr;

while ((seg = next_segment(len, offset)) != 0) {
npages = get_user_pages_unlocked(hva, 1, &page, FOLL_KVM);
if (npages != 1)
return -EFAULT;
- memcpy(data, page_address(page) + offset, seg);
+
+ vaddr = map_page_atomic(page);
+ memcpy(data, vaddr + offset, seg);
+ unmap_page_atomic(vaddr);
+
put_page(page);
len -= seg;
hva += seg;
@@ -2283,13 +2311,18 @@ int copy_to_guest(unsigned long hva, const void *data, int len)
int offset = offset_in_page(hva);
struct page *page;
int npages, seg;
+ void *vaddr;

while ((seg = next_segment(len, offset)) != 0) {
npages = get_user_pages_unlocked(hva, 1, &page,
FOLL_WRITE | FOLL_KVM);
if (npages != 1)
return -EFAULT;
- memcpy(page_address(page) + offset, data, seg);
+
+ vaddr = map_page_atomic(page);
+ memcpy(vaddr + offset, data, seg);
+ unmap_page_atomic(vaddr);
+
put_page(page);
len -= seg;
hva += seg;
@@ -4921,6 +4954,18 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
if (r)
goto out_free;

+ if (VM_KVM_PROTECTED) {
+ guest_map_ptes = kmalloc_array(num_possible_cpus(),
+ sizeof(pte_t *), GFP_KERNEL);
+ if (!guest_map_ptes)
+ goto out_unreg;
+
+ guest_map_area = alloc_vm_area(PAGE_SIZE * num_possible_cpus(),
+ guest_map_ptes);
+ if (!guest_map_ptes)
+ goto out_unreg;
+ }
+
kvm_chardev_ops.owner = module;
kvm_vm_fops.owner = module;
kvm_vcpu_fops.owner = module;
@@ -4944,6 +4989,10 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
return 0;

out_unreg:
+ if (guest_map_area)
+ free_vm_area(guest_map_area);
+ if (guest_map_ptes)
+ kfree(guest_map_ptes);
kvm_async_pf_deinit();
out_free:
kmem_cache_destroy(kvm_vcpu_cache);
@@ -4965,6 +5014,10 @@ EXPORT_SYMBOL_GPL(kvm_init);

void kvm_exit(void)
{
+ if (guest_map_area)
+ free_vm_area(guest_map_area);
+ if (guest_map_ptes)
+ kfree(guest_map_ptes);
debugfs_remove_recursive(kvm_debugfs_dir);
misc_deregister(&kvm_dev);
kmem_cache_destroy(kvm_vcpu_cache);
--
2.26.2