kvm: mmu: don't do memslot overflow check

As Andres pointed out:

| I don't understand the value of this check here. Are we looking for a
| broken memslot? Shouldn't this be a BUG_ON? Is this the place to care
| about these things? npages is capped to KVM_MEM_MAX_NR_PAGES, i.e.
| 2^31. A 64 bit overflow would be caused by a gigantic gfn_start which
| would be trouble in many other ways.

This patch drops the memslot overflow check to make the codes more simple.

Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Message-Id: <1429064694-3072-1-git-send-email-wanpeng.li@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 146f295ee32214a6f4ad40a58e53b61a3d1fa06d..07bb22157338ddfd4723f4007483d76a0e1b16d7 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4504,19 +4504,12 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
        bool flush = false;
        unsigned long *rmapp;
        unsigned long last_index, index;
-       gfn_t gfn_start, gfn_end;
 
        spin_lock(&kvm->mmu_lock);
 
-       gfn_start = memslot->base_gfn;
-       gfn_end = memslot->base_gfn + memslot->npages - 1;
-
-       if (gfn_start >= gfn_end)
-               goto out;
-
        rmapp = memslot->arch.rmap[0];
-       last_index = gfn_to_index(gfn_end, memslot->base_gfn,
-                                       PT_PAGE_TABLE_LEVEL);
+       last_index = gfn_to_index(memslot->base_gfn + memslot->npages - 1,
+                               memslot->base_gfn, PT_PAGE_TABLE_LEVEL);
 
        for (index = 0; index <= last_index; ++index, ++rmapp) {
                if (*rmapp)
@@ -4534,7 +4527,6 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
        if (flush)
                kvm_flush_remote_tlbs(kvm);
 
-out:
        spin_unlock(&kvm->mmu_lock);
 }