diff options
| author | Sean Christopherson <seanjc@google.com> | 2025-10-30 13:09:37 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2025-11-05 11:05:52 -0800 |
| commit | af96d5452e5e88019bed9c081d4be1c489d7c081 (patch) | |
| tree | f64af395dc174ca09e5f4d061349c1d349231386 | |
| parent | 24adff39705223f06607926f2717e6f8dec12d28 (diff) | |
KVM: TDX: Use atomic64_dec_return() instead of a poor equivalent
Use atomic64_dec_return() when decrementing the number of "pre-mapped"
S-EPT pages to ensure that the count can't go negative without KVM
noticing. In theory, checking for '0' and then decrementing in a separate
operation could miss a 0=>-1 transition. In practice, such a condition is
impossible because nr_premapped is protected by slots_lock, i.e. doesn't
actually need to be an atomic (that wart will be addressed shortly).
Don't bother trying to keep the count non-negative, as the KVM_BUG_ON()
ensures the VM is dead, i.e. there's no point in trying to limp along.
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030200951.3402865-15-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
| -rw-r--r-- | arch/x86/kvm/vmx/tdx.c | 6 |
1 files changed, 2 insertions, 4 deletions
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 4426146d403e..8482eadbbb8f 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -1726,10 +1726,9 @@ static int tdx_sept_zap_private_spte(struct kvm *kvm, gfn_t gfn, tdx_no_vcpus_enter_stop(kvm); } if (tdx_is_sept_zap_err_due_to_premap(kvm_tdx, err, entry, level)) { - if (KVM_BUG_ON(!atomic64_read(&kvm_tdx->nr_premapped), kvm)) + if (KVM_BUG_ON(atomic64_dec_return(&kvm_tdx->nr_premapped) < 0, kvm)) return -EIO; - atomic64_dec(&kvm_tdx->nr_premapped); return 0; } @@ -3171,8 +3170,7 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, goto out; } - if (!KVM_BUG_ON(!atomic64_read(&kvm_tdx->nr_premapped), kvm)) - atomic64_dec(&kvm_tdx->nr_premapped); + KVM_BUG_ON(atomic64_dec_return(&kvm_tdx->nr_premapped) < 0, kvm); if (arg->flags & KVM_TDX_MEASURE_MEMORY_REGION) { for (i = 0; i < PAGE_SIZE; i += TDX_EXTENDMR_CHUNKSIZE) { |