Messages in this thread | | | Date | Wed, 22 Nov 2023 10:18:47 +0800 | Subject | Re: [PATCH v6 11/16] KVM: x86/tdp_mmu: Split the large page when zap leaf | From | Binbin Wu <> |
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On 11/21/2023 7:00 PM, Isaku Yamahata wrote: > On Tue, Nov 21, 2023 at 05:57:28PM +0800, > Binbin Wu <binbin.wu@linux.intel.com> wrote: > >>> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c >>> index 7873e9ee82ad..a209a67decae 100644 >>> --- a/arch/x86/kvm/mmu/tdp_mmu.c >>> +++ b/arch/x86/kvm/mmu/tdp_mmu.c >>> @@ -964,6 +964,14 @@ bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp) >>> return true; >>> } >>> + >>> +static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(struct kvm *kvm, >>> + struct tdp_iter *iter, >>> + bool shared); >>> + >>> +static int tdp_mmu_split_huge_page(struct kvm *kvm, struct tdp_iter *iter, >>> + struct kvm_mmu_page *sp, bool shared); >>> + >>> /* >>> * If can_yield is true, will release the MMU lock and reschedule if the >>> * scheduler needs the CPU or there is contention on the MMU lock. If this >>> @@ -975,13 +983,15 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, >>> gfn_t start, gfn_t end, bool can_yield, bool flush, >>> bool zap_private) >>> { >>> + bool is_private = is_private_sp(root); >>> + struct kvm_mmu_page *split_sp = NULL; >>> struct tdp_iter iter; >>> end = min(end, tdp_mmu_max_gfn_exclusive()); >>> lockdep_assert_held_write(&kvm->mmu_lock); >>> - WARN_ON_ONCE(zap_private && !is_private_sp(root)); >>> + WARN_ON_ONCE(zap_private && !is_private); >>> if (!zap_private && is_private_sp(root)) >> Can use is_private instead of is_private_sp(root) here as well. > I'll update it. > >>> return false; >>> @@ -1006,12 +1016,66 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, >>> !is_last_spte(iter.old_spte, iter.level)) >>> continue; >>> + if (is_private && kvm_gfn_shared_mask(kvm) && >>> + is_large_pte(iter.old_spte)) { >>> + gfn_t gfn = iter.gfn & ~kvm_gfn_shared_mask(kvm); >>> + gfn_t mask = KVM_PAGES_PER_HPAGE(iter.level) - 1; >>> + struct kvm_memory_slot *slot; >>> + struct kvm_mmu_page *sp; >>> + >>> + slot = gfn_to_memslot(kvm, gfn); >>> + if (kvm_hugepage_test_mixed(slot, gfn, iter.level) || >>> + (gfn & mask) < start || >>> + end < (gfn & mask) + KVM_PAGES_PER_HPAGE(iter.level)) { >>> + WARN_ON_ONCE(!can_yield); >>> + if (split_sp) { >>> + sp = split_sp; >>> + split_sp = NULL; >>> + sp->role = tdp_iter_child_role(&iter); >>> + } else { >>> + WARN_ON(iter.yielded); >>> + if (flush && can_yield) { >>> + kvm_flush_remote_tlbs(kvm); >>> + flush = false; >>> + } >> Is it necessary to do the flush here? > Because tdp_mmu_alloc_sp_for_split() may unlock mmu_lock and block. > While blocking, other thread operates on KVM MMU and gets confused due to > remaining TLB cache. > > >>> + sp = tdp_mmu_alloc_sp_for_split(kvm, &iter, false); >>> + if (iter.yielded) { >>> + split_sp = sp; >>> + continue; >>> + } >>> + } >>> + KVM_BUG_ON(!sp, kvm); >>> + >>> + tdp_mmu_init_sp(sp, iter.sptep, iter.gfn); >>> + if (tdp_mmu_split_huge_page(kvm, &iter, sp, false)) { >>> + kvm_flush_remote_tlbs(kvm); >>> + flush = false; >> Why it needs to flush TLB immediately if tdp_mmu_split_huge_page() fails? > Hmm, we don't need it. When breaking up page table, we need to tlb flush > before issuing TDH.MEM.PAGE.DEMOTE(), not after it. Will remove those two lines. > > >> Also, when KVM MMU write lock is held, it seems tdp_mmu_split_huge_page() >> will not fail. > This can happen with TDX_OPERAND_BUSY with secure-ept tree lock with other > vcpus TDH.VP.ENTER(). TDH.VP.ENTER() can take exclusive lock of secure-EPT. > > >> But let's assume this condition can be triggered, since sp is >> local >> variable, it will lost its value after continue, and split_sp is also NULL, >> it will try to allocate a new sp, memory leakage here? > Nice catch. I'll add split_sp = sp; > > >>> + /* force retry on this gfn. */ >>> + iter.yielded = true; >>> + } else >>> + flush = true; >>> + continue; >>> + } >>> + } >>> + >>> tdp_mmu_iter_set_spte(kvm, &iter, SHADOW_NONPRESENT_VALUE); >>> flush = true; >>> } >>> rcu_read_unlock(); >>> + if (split_sp) { >>> + WARN_ON(!can_yield); >>> + if (flush) { >>> + kvm_flush_remote_tlbs(kvm); >>> + flush = false; >>> + } >> Same here, why we need to do the flush here? >> Can we delay it till the caller do the flush? > No. Because we unlock mmu_lock and may block when freeing memory. But I don't find it may block during freeing memory. Did I miss anything?
> >>> + >>> + write_unlock(&kvm->mmu_lock); >>> + tdp_mmu_free_sp(split_sp); >>> + write_lock(&kvm->mmu_lock); >>> + } >>> + >>> /* >>> * Because this flow zaps _only_ leaf SPTEs, the caller doesn't need >>> * to provide RCU protection as no 'struct kvm_mmu_page' will be freed. >>> @@ -1606,8 +1670,6 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(struct kvm *kvm, >>> KVM_BUG_ON(kvm_mmu_page_role_is_private(role) != >>> is_private_sptep(iter->sptep), kvm); >>> - /* TODO: Large page isn't supported for private SPTE yet. */ >>> - KVM_BUG_ON(kvm_mmu_page_role_is_private(role), kvm); >>> /* >>> * Since we are allocating while under the MMU lock we have to be >>
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