This patch set aims to fix a bug in which KVM incorrectly assumes a large page as a NX huge page. The bug would prevent guest VM from regaining large pages and cause performance issue. We fix the bug by explicitly checking the lpage_disallowed field in the shadow page. Moreover, to fix the bug properly for TDP MMU, we integrate two patches from Sean that ensures that we update lpage_disallowed in shadow page before making spte visible to guest. To verify the bug fixed, we use dirty logging as the testing target and dirty_log_perf_test as the selftest binary. By adding the code to check the page stats from the per-VM interface, we discovered that VMs could regain large pages after dirty logging disabled. We also verify the existence of the bug if running with unpatched kernels. To make the selftest working properly with per-VM stats interface, we borrowes two patches come from Ben's series: "[PATCH 00/13] KVM: x86: Add a cap to disable NX hugepages on a VM" [1]. [1] https://lore.kernel.org/all/20220310164532.1821490-2-bgardon@xxxxxxxxxx/T/ v2 -> v3: - Update lpage_disallowed before making spte visible [seanjc]. - Adding tdp_mmu_pages stats [seanjc] - update comments in selftest [bgardon] v2: https://lore.kernel.org/lkml/20220323184915.1335049-1-mizhang@xxxxxxxxxx/T/ v1 -> v2: - Update the commit message. [dmatlack] - Update the comments in patch 3/4 to clarify the motivation. [bgardon] - Add another iteration in dirty_log_perf_test to regain pages [bgardon] Ben Gardon (2): KVM: selftests: Dump VM stats in binary stats test KVM: selftests: Test reading a single stat Mingwei Zhang (2): KVM: x86/mmu: explicitly check nx_hugepage in disallowed_hugepage_adjust() selftests: KVM: use page stats to check if dirty logging works properly Sean Christopherson (2): KVM: x86/mmu: Set lpage_disallowed in TDP MMU before setting SPTE KVM: x86/mmu: Track the number of TDP MMU pages, but not the actual pages arch/x86/include/asm/kvm_host.h | 11 +- arch/x86/kvm/mmu/mmu.c | 28 ++- arch/x86/kvm/mmu/mmu_internal.h | 2 +- arch/x86/kvm/mmu/tdp_mmu.c | 36 ++-- .../selftests/kvm/dirty_log_perf_test.c | 53 +++++ .../selftests/kvm/include/kvm_util_base.h | 2 + .../selftests/kvm/kvm_binary_stats_test.c | 6 + tools/testing/selftests/kvm/lib/kvm_util.c | 196 ++++++++++++++++++ 8 files changed, 303 insertions(+), 31 deletions(-) -- 2.35.1.1094.g7c7d902a7c-goog
