Messages in this thread | | | Date | Tue, 21 Nov 2023 17:57:28 +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 11/7/2023 11:00 PM, isaku.yamahata@intel.com wrote: > From: Xiaoyao Li <xiaoyao.li@intel.com> > > When TDX enabled, a large page cannot be zapped if it contains mixed > pages. In this case, it has to split the large page. > > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com> > --- > arch/x86/kvm/Kconfig | 1 + > arch/x86/kvm/mmu/mmu.c | 6 +-- > arch/x86/kvm/mmu/mmu_internal.h | 9 +++++ > arch/x86/kvm/mmu/tdp_mmu.c | 68 +++++++++++++++++++++++++++++++-- > 4 files changed, 78 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig > index b0f103641547..557479737962 100644 > --- a/arch/x86/kvm/Kconfig > +++ b/arch/x86/kvm/Kconfig > @@ -93,6 +93,7 @@ config KVM_INTEL > tristate "KVM for Intel (and compatible) processors support" > depends on KVM && IA32_FEAT_CTL > select KVM_SW_PROTECTED_VM if INTEL_TDX_HOST > + select KVM_GENERIC_MEMORY_ATTRIBUTES if INTEL_TDX_HOST > select KVM_PRIVATE_MEM if INTEL_TDX_HOST > help > Provides support for KVM on processors equipped with Intel's VT > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 265177cedf37..0bf043812644 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -7463,8 +7463,8 @@ bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm, > return kvm_unmap_gfn_range(kvm, range); > } > > -static bool hugepage_test_mixed(struct kvm_memory_slot *slot, gfn_t gfn, > - int level) > +bool kvm_hugepage_test_mixed(struct kvm_memory_slot *slot, gfn_t gfn, > + int level) > { > return lpage_info_slot(gfn, slot, level)->disallow_lpage & KVM_LPAGE_MIXED_FLAG; > } > @@ -7491,7 +7491,7 @@ static bool hugepage_has_attrs(struct kvm *kvm, struct kvm_memory_slot *slot, > return kvm_range_has_memory_attributes(kvm, start, end, attrs); > > for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1)) { > - if (hugepage_test_mixed(slot, gfn, level - 1) || > + if (kvm_hugepage_test_mixed(slot, gfn, level - 1) || > attrs != kvm_get_memory_attributes(kvm, gfn)) > return false; > } > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h > index 1da98be74ad2..653e96769956 100644 > --- a/arch/x86/kvm/mmu/mmu_internal.h > +++ b/arch/x86/kvm/mmu/mmu_internal.h > @@ -460,4 +460,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc); > void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp); > void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp); > > +#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES > +bool kvm_hugepage_test_mixed(struct kvm_memory_slot *slot, gfn_t gfn, int level); > +#else > +static inline bool kvm_hugepage_test_mixed(struct kvm_memory_slot *slot, gfn_t gfn, int level) > +{ > + return false; > +} > +#endif > + > #endif /* __KVM_X86_MMU_INTERNAL_H */ > 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.
> 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?
> + 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?
Also, when KVM MMU write lock is held, it seems tdp_mmu_split_huge_page() will not fail. 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?
> + /* 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?
> + > + 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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