[PATCH 3.16.y-ckt 163/180] KVM: use slowpath for cross page cached accesses

[Luis Henriques]

3.16.7-ckt11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@xxxxxxxxxx>

commit ca3f0874723fad81d0c701b63ae3a17a408d5f25 upstream.

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 KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Message-Id: <20150408121648.GA3519@xxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 virt/kvm/kvm_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 27e140d5f073..032150ca597d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1550,8 +1550,8 @@ 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 {
 		/*
--
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