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Subject[PATCH 5.0 175/238] Revert "KVM/MMU: Flush tlb directly in the kvm_zap_gfn_range()"
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

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

From: Ben Gardon <bgardon@google.com>

commit 92da008fa21034c369cdb8ca2b629fe5c196826b upstream.

This reverts commit 71883a62fcd6c70639fa12cda733378b4d997409.

The above commit contains an optimization to kvm_zap_gfn_range which
uses gfn-limited TLB flushes, if enabled. If using these limited flushes,
kvm_zap_gfn_range passes lock_flush_tlb=false to slot_handle_level_range
which creates a race when the function unlocks to call cond_resched.
See an example of this race below:

CPU 0 CPU 1 CPU 3
// zap_direct_gfn_range
mmu_lock()
// *ptep == pte_1
*ptep = 0
if (lock_flush_tlb)
flush_tlbs()
mmu_unlock()
// In invalidate range
// MMU notifier
mmu_lock()
if (pte != 0)
*ptep = 0
flush = true
if (flush)
flush_remote_tlbs()
mmu_unlock()
return
// Host MM reallocates
// page previously
// backing guest memory.
// Guest accesses
// invalid page
// through pte_1
// in its TLB!!

Tested: Ran all kvm-unit-tests on a Intel Haswell machine with and
without this patch. The patch introduced no new failures.

Signed-off-by: Ben Gardon <bgardon@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/mmu.c | 16 +++-------------
1 file changed, 3 insertions(+), 13 deletions(-)

--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5635,13 +5635,8 @@ void kvm_zap_gfn_range(struct kvm *kvm,
{
struct kvm_memslots *slots;
struct kvm_memory_slot *memslot;
- bool flush_tlb = true;
- bool flush = false;
int i;

- if (kvm_available_flush_tlb_with_range())
- flush_tlb = false;
-
spin_lock(&kvm->mmu_lock);
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
slots = __kvm_memslots(kvm, i);
@@ -5653,17 +5648,12 @@ void kvm_zap_gfn_range(struct kvm *kvm,
if (start >= end)
continue;

- flush |= slot_handle_level_range(kvm, memslot,
- kvm_zap_rmapp, PT_PAGE_TABLE_LEVEL,
- PT_MAX_HUGEPAGE_LEVEL, start,
- end - 1, flush_tlb);
+ slot_handle_level_range(kvm, memslot, kvm_zap_rmapp,
+ PT_PAGE_TABLE_LEVEL, PT_MAX_HUGEPAGE_LEVEL,
+ start, end - 1, true);
}
}

- if (flush)
- kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
- gfn_end - gfn_start + 1);
-
spin_unlock(&kvm->mmu_lock);
}


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