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KVM: x86/mmu: do not allow readers to acquire references to invalid roots 

Remove the "shared" argument of for_each_tdp_mmu_root_yield_safe, thus ensuring
that readers do not ever acquire a reference to an invalid root.  After this
patch, all readers except kvm_tdp_mmu_zap_invalidated_roots() treat
refcount=0/valid, refcount=0/invalid and refcount=1/invalid in exactly the
same way.  kvm_tdp_mmu_zap_invalidated_roots() is different but it also
does not acquire a reference to the invalid root, and it cannot see
refcount=0/invalid because it is guaranteed to run after
kvm_tdp_mmu_invalidate_all_roots().

Opportunistically add a lockdep assertion to the yield-safe iterator.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2022-03-02 08:51:05 -05:00
parent 7c554d8e51
commit 614f6970aa
1 changed files with 5 additions and 4 deletions
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9
arch/x86/kvm/mmu/tdp_mmu.c
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@ -166,14 +166,15 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, _only_valid); \
_root; \
_root = tdp_mmu_next_root(_kvm, _root, _shared, _only_valid)) \
if (kvm_mmu_page_as_id(_root) != _as_id) { \
if (kvm_lockdep_assert_mmu_lock_held(_kvm, _shared) && \
kvm_mmu_page_as_id(_root) != _as_id) { \
} else
#define for_each_valid_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared) \
__for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, true)
#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared) \
__for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, false)
#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id) \
__for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, false, false)
/*
* Iterate over all TDP MMU roots. Requires that mmu_lock be held for write,
@ -808,7 +809,7 @@ bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, gfn_t start,
{
struct kvm_mmu_page *root;
for_each_tdp_mmu_root_yield_safe(kvm, root, as_id, false)
for_each_tdp_mmu_root_yield_safe(kvm, root, as_id)
flush = zap_gfn_range(kvm, root, start, end, can_yield, flush,
false);