Split NX huge page recovery in two separate flows, one for TDP MMU and one for non-TDP MMU. TDP MMU flow will use MMU read lock and non-TDP MMU flow will use MMU write lock. This change unblocks vCPUs which are waiting for MMU read lock while NX huge page recovery is running and zapping shadow pages. A Windows guest was showing network latency jitters which was root caused to vCPUs waiting for MMU read lock when NX huge page recovery thread was holding MMU write lock. Disabling NX huge page recovery fixed the jitter issue. So, to optimize NX huge page recovery, it was modified to run under MMU read lock, the switch made jitter issue disappear completely and vCPUs wait time for MMU read lock reduced drastically. Patch 4 commit log has the data from the tool to show improvement observed. Patch 1 adds a little bit of code churn which is removed in Patch 2 and 3. It was done to make tracking NX huge pages separately in a separate patch and then later split common recovery worker code. v2: - Track legacy and TDP MMU NX huge pages separately. - Each list has their own calculation of "to_zap", i.e. number of pages to zap. - Unaccount huge page before dirty log check and zap logic in TDP MMU recovery worker. Check patch 4 for more details. - 32 bit build issue fix. - Sparse warning fix for comparing RCU pointer with non-RCU pointer. (sp->spt == spte_to_child_pt()) v1: https://lore.kernel.org/kvm/20240812171341.1763297-1-vipinsh@xxxxxxxxxx/#t Vipin Sharma (4): KVM: x86/mmu: Track TDP MMU NX huge pages separately KVM: x86/mmu: Extract out TDP MMU NX huge page recovery code KVM: x86/mmu: Rearrange locks and to_zap count for NX huge page recovery KVM: x86/mmu: Recover TDP MMU NX huge pages using MMU read lock arch/x86/include/asm/kvm_host.h | 13 ++- arch/x86/kvm/mmu/mmu.c | 135 +++++++++++++++++--------------- arch/x86/kvm/mmu/mmu_internal.h | 3 + arch/x86/kvm/mmu/tdp_mmu.c | 122 +++++++++++++++++++++++++++-- arch/x86/kvm/mmu/tdp_mmu.h | 3 +- 5 files changed, 204 insertions(+), 72 deletions(-) base-commit: 332d2c1d713e232e163386c35a3ba0c1b90df83f -- 2.46.0.469.g59c65b2a67-goog
