KVM: use slowpath for cross page cached accesses

kvm_write_guest_cached() does not mark all written pages as dirty and
code comments in kvm_gfn_to_hva_cache_init() talk about NULL memslot
with cross page accesses.  Fix all the easy way.

The check is '<= 1' to have the same result for 'len = 0' cache anywhere
in the page.  (nr_pages_needed is 0 on page boundary.)

Fixes: 8f964525a121 ("KVM: Allow cross page reads and writes from cached translations.")
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Message-Id: <20150408121648.GA3519@potion.brq.redhat.com>
Reviewed-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index aadef264bed1..91a36e21c0fb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1637,8 +1637,8 @@ int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
         ghc->generation = slots->generation;
         ghc->len = len;
         ghc->memslot = gfn_to_memslot(kvm, start_gfn);
-        ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn, &nr_pages_avail);
-        if (!kvm_is_error_hva(ghc->hva) && nr_pages_avail >= nr_pages_needed) {
+        ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn, NULL);
+        if (!kvm_is_error_hva(ghc->hva) && nr_pages_needed <= 1) {
                 ghc->hva += offset;
         } else {
                 /*