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KVM: x86/mmu: Fix RCU usage in handle_removed_tdp_mmu_page 

The pt passed into handle_removed_tdp_mmu_page does not need RCU
protection, as it is not at any risk of being freed by another thread at
that point. However, the implicit cast from tdp_sptep_t to u64 * dropped
the __rcu annotation without a proper rcu_derefrence. Fix this by
passing the pt as a tdp_ptep_t and then rcu_dereferencing it in
the function.

Suggested-by: Sean Christopherson <seanjc@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210315233803.2706477-2-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Ben Gardon 2021-03-15 16:38:00 -07:00 committed by Paolo Bonzini
parent 1e28eed176
commit 70fb3e41a9
1 changed files with 8 additions and 3 deletions
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11
arch/x86/kvm/mmu/tdp_mmu.c
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@ -301,11 +301,16 @@ static void tdp_mmu_unlink_page(struct kvm *kvm, struct kvm_mmu_page *sp,
*
* Given a page table that has been removed from the TDP paging structure,
* iterates through the page table to clear SPTEs and free child page tables.
*
* Note that pt is passed in as a tdp_ptep_t, but it does not need RCU
* protection. Since this thread removed it from the paging structure,
* this thread will be responsible for ensuring the page is freed. Hence the
* early rcu_dereferences in the function.
*/
static void handle_removed_tdp_mmu_page(struct kvm *kvm, u64 *pt,
static void handle_removed_tdp_mmu_page(struct kvm *kvm, tdp_ptep_t pt,
bool shared)
{
struct kvm_mmu_page *sp = sptep_to_sp(pt);
struct kvm_mmu_page *sp = sptep_to_sp(rcu_dereference(pt));
int level = sp->role.level;
gfn_t base_gfn = sp->gfn;
u64 old_child_spte;
@ -318,7 +323,7 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, u64 *pt,
tdp_mmu_unlink_page(kvm, sp, shared);
for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
sptep = pt + i;
sptep = rcu_dereference(pt) + i;
gfn = base_gfn + (i * KVM_PAGES_PER_HPAGE(level - 1));
if (shared) {