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AJvYcCVVO2FocuBZ3d7bIDqSKP/1YrBxITm5CrgdvUckvVOsGX+Q4t4/i+M9r1lWBhEYT72eZSisFCa+6Km6Bko=@vger.kernel.org X-Gm-Message-State: AOJu0YykxKCLJ7CcQgo78jsRyqdo+f4FPdYWqMeEfXNHKnLTimwHbi8S rXY8RIeZy5tGGRcOtBtgRFAqrLEgDlQ/1jrvaySckdh3Zw2fo/FDPo9qiTBWShc9XZKO3Vzhx0l 7byuCNA== X-Received: from pgax34.prod.google.com ([2002:a05:6a02:2e62:b0:c65:c5fc:1707]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7fa9:b0:366:14ac:e20a with SMTP id adf61e73a8af0-393af2a3f9amr3224489637.72.1770394148215; Fri, 06 Feb 2026 08:09:08 -0800 (PST) Date: Fri, 6 Feb 2026 08:09:06 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260129011517.3545883-1-seanjc@google.com> <20260129011517.3545883-38-seanjc@google.com> Message-ID: Subject: Re: [RFC PATCH v5 37/45] KVM: x86/tdp_mmu: Alloc external_spt page for mirror page table splitting From: Sean Christopherson To: Yan Zhao Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Paolo Bonzini , linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, Kai Huang , Rick Edgecombe , Vishal Annapurve , Ackerley Tng , Sagi Shahar , Binbin Wu , Xiaoyao Li , Isaku Yamahata Content-Type: text/plain; charset="us-ascii" On Fri, Feb 06, 2026, Yan Zhao wrote: > On Wed, Jan 28, 2026 at 05:15:09PM -0800, Sean Christopherson wrote: > > From: Isaku Yamahata > > > > Enhance tdp_mmu_alloc_sp_for_split() to allocate a page table page for the > > external page table for splitting the mirror page table. > > > > Signed-off-by: Isaku Yamahata > > Co-developed-by: Yan Zhao > > Signed-off-by: Yan Zhao > > [sean: use kvm_x86_ops.alloc_external_sp()] > > Signed-off-by: Sean Christopherson > > --- > > arch/x86/kvm/mmu/tdp_mmu.c | 13 +++++++++++-- > > 1 file changed, 11 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > > index 3b0da898824a..4f5b80f0ca03 100644 > > --- a/arch/x86/kvm/mmu/tdp_mmu.c > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > > @@ -1447,7 +1447,7 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm, > > return spte_set; > > } > > > > -static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void) > > +static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(struct tdp_iter *iter) > > { > > struct kvm_mmu_page *sp; > > > > @@ -1461,6 +1461,15 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void) > > return NULL; > > } > > > > + if (is_mirror_sptep(iter->sptep)) { > tdp_mmu_alloc_sp_for_split() is invoked in tdp_mmu_split_huge_pages_root() after > rcu_read_unlock() is called. > > So, it's incorrect to invoke is_mirror_sptep() which internally contains > rcu_dereference(), resulting in "WARNING: suspicious RCU usage". Ah, now I see why the previous code pass in a bool. I don't love passing a bool, but passing @iter is outright dangerous, so I guess this? diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index a32192c35099..4d92c0d19d7c 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1448,7 +1448,7 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm, } static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(struct kvm *kvm, - struct tdp_iter *iter) + bool is_mirror_sp) { struct kvm_mmu_page *sp; @@ -1460,7 +1460,7 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(struct kvm *kvm, if (!sp->spt) goto err_spt; - if (is_mirror_sptep(iter->sptep)) { + if (is_mirror_sp) { sp->external_spt = (void *)kvm_x86_call(alloc_external_sp)(GFP_KERNEL_ACCOUNT); if (!sp->external_spt) goto err_external_spt; @@ -1525,6 +1525,7 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm, gfn_t start, gfn_t end, int target_level, bool shared) { + const bool is_mirror_root = is_mirror_sp(root); struct kvm_mmu_page *sp = NULL; struct tdp_iter iter; @@ -1557,7 +1558,7 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm, else write_unlock(&kvm->mmu_lock); - sp = tdp_mmu_alloc_sp_for_split(kvm, &iter); + sp = tdp_mmu_alloc_sp_for_split(kvm, is_mirror_root); if (shared) read_lock(&kvm->mmu_lock);