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authorBen Gardon <bgardon@google.com>2021-03-16 00:38:00 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2021-03-16 19:14:59 +0100
commit70fb3e41a97a5fecc0aedc9a429479d702c3ab66 (patch)
treec3ce4eb0ec0285287493b9ce648050e44f5976b9 /arch
parentLinux 5.12-rc3 (diff)
downloadlinux-70fb3e41a97a5fecc0aedc9a429479d702c3ab66.tar.xz
linux-70fb3e41a97a5fecc0aedc9a429479d702c3ab66.zip
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>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/mmu/tdp_mmu.c11
1 files changed, 8 insertions, 3 deletions
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index d78915019b08..db2936cca4bf 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -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) {