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KVM: x86/mmu: Mark SPTEs in disconnected pages as removed

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When clearing TDP MMU pages what have been disconnected from the paging
structure root, set the SPTEs to a special non-present value which will
not be overwritten by other threads. This is needed to prevent races in
which a thread is clearing a disconnected page table, but another thread
has already acquired a pointer to that memory and installs a mapping in
an already cleared entry. This can lead to memory leaks and accounting
errors.

Reviewed-by: Peter Feiner <pfeiner@google.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210202185734.1680553-23-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Ben Gardon 2021-02-02 10:57:28 -08:00 committed by Paolo Bonzini
parent 08f07c800e
commit e25f0e0cd5
1 changed files with 30 additions and 6 deletions
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36
arch/x86/kvm/mmu/tdp_mmu.c
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@ -334,9 +334,10 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, u64 *pt,
{
struct kvm_mmu_page *sp = sptep_to_sp(pt);
int level = sp->role.level;
gfn_t gfn = sp->gfn;
gfn_t base_gfn = sp->gfn;
u64 old_child_spte;
u64 *sptep;
gfn_t gfn;
int i;
trace_kvm_mmu_prepare_zap_page(sp);
@ -345,16 +346,39 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, u64 *pt,
for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
sptep = pt + i;
gfn = base_gfn + (i * KVM_PAGES_PER_HPAGE(level - 1));
if (shared) {
old_child_spte = xchg(sptep, 0);
/*
* Set the SPTE to a nonpresent value that other
* threads will not overwrite. If the SPTE was
* already marked as removed then another thread
* handling a page fault could overwrite it, so
* set the SPTE until it is set from some other
* value to the removed SPTE value.
*/
for (;;) {
old_child_spte = xchg(sptep, REMOVED_SPTE);
if (!is_removed_spte(old_child_spte))
break;
cpu_relax();
}
} else {
old_child_spte = READ_ONCE(*sptep);
WRITE_ONCE(*sptep, 0);
/*
* Marking the SPTE as a removed SPTE is not
* strictly necessary here as the MMU lock will
* stop other threads from concurrently modifying
* this SPTE. Using the removed SPTE value keeps
* the two branches consistent and simplifies
* the function.
*/
WRITE_ONCE(*sptep, REMOVED_SPTE);
}
handle_changed_spte(kvm, kvm_mmu_page_as_id(sp),
gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)),
old_child_spte, 0, level - 1, shared);
handle_changed_spte(kvm, kvm_mmu_page_as_id(sp), gfn,
old_child_spte, REMOVED_SPTE, level - 1,
shared);
}
kvm_flush_remote_tlbs_with_address(kvm, gfn,