From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 356C1C5ACB3 for ; Tue, 21 Nov 2023 11:01:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233769AbjKULBk (ORCPT ); Tue, 21 Nov 2023 06:01:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234147AbjKULBZ (ORCPT ); Tue, 21 Nov 2023 06:01:25 -0500 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 854F610F9; Tue, 21 Nov 2023 03:00:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1700564447; x=1732100447; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=NcRwqwQTwQ6onun3MTTPMLU8sOfAkpxdSQyc+TxerF0=; b=ZFoI5/zTlJWERs04X0S9hDE0/8EAzzUIV0jN9FOXzp71pI9DPIwvGwtN evK/mjVNjVArwvWskLhtPDuGLOu542EcBJfbPgLaOuuy2bmUtULy78cJX BOOxc99KLqMbhAud5DR1hCkn6XDUqMECxdofADMpnHuHvtFeCmX/u/lCy woxGYpDzstAszbgWEvXfLhqEpN2m1arLXyMT/SaJa4jRwRVfoR0nbkpj6 RjTQWQ/v8wcs7iml42+1lCRg2oImLlhoZG61kiWYwXDMd3oGrnWEUDrM5 Q+KixSdTb9nWm+CGDIwbapwJ5mwGE/TTz27tEk7237EuN+DyhciEEVVRx g==; X-IronPort-AV: E=McAfee;i="6600,9927,10900"; a="382209974" X-IronPort-AV: E=Sophos;i="6.04,215,1695711600"; d="scan'208";a="382209974" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Nov 2023 03:00:46 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10900"; a="766607182" X-IronPort-AV: E=Sophos;i="6.04,215,1695711600"; d="scan'208";a="766607182" Received: from ls.sc.intel.com (HELO localhost) ([172.25.112.31]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Nov 2023 03:00:46 -0800 Date: Tue, 21 Nov 2023 03:00:45 -0800 From: Isaku Yamahata To: Binbin Wu Cc: isaku.yamahata@intel.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com, Paolo Bonzini , erdemaktas@google.com, Sean Christopherson , Sagi Shahar , David Matlack , Kai Huang , Zhi Wang , chen.bo@intel.com, hang.yuan@intel.com, tina.zhang@intel.com, Xiaoyao Li , isaku.yamahata@linux.intel.com Subject: Re: [PATCH v6 11/16] KVM: x86/tdp_mmu: Split the large page when zap leaf Message-ID: <20231121110045.GH1109547@ls.amr.corp.intel.com> References: <8b43a9203c34b5330c4ea5901da5dac3458ac98d.1699368363.git.isaku.yamahata@intel.com> <5d9aadbd-975b-4c4d-ba18-ac6e0fb07ba1@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <5d9aadbd-975b-4c4d-ba18-ac6e0fb07ba1@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 21, 2023 at 05:57:28PM +0800, Binbin Wu 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. > > + > > + 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 > > -- Isaku Yamahata