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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id o26sm7272353ejx.90.2021.04.08.05.09.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Apr 2021 05:09:10 -0700 (PDT) Subject: Re: [PATCH v2 07/17] KVM: x86/mmu: Check PDPTRs before allocating PAE roots To: Wanpeng Li , Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm , LKML , Ben Gardon , Brijesh Singh , Tom Lendacky References: <20210305011101.3597423-1-seanjc@google.com> <20210305011101.3597423-8-seanjc@google.com> From: Paolo Bonzini Message-ID: Date: Thu, 8 Apr 2021 14:09:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/04/21 13:15, Wanpeng Li wrote: > I saw this splatting: > > BUG: sleeping function called from invalid context at > arch/x86/kvm/kvm_cache_regs.h:115 > kvm_pdptr_read+0x20/0x60 [kvm] > kvm_mmu_load+0x3bd/0x540 [kvm] > > There is a might_sleep() in kvm_pdptr_read(), however, the original > commit didn't explain more. I can send a formal one if the below fix > is acceptable. I think we can just push make_mmu_pages_available down into kvm_mmu_load's callees. This way it's not necessary to hold the lock until after the PDPTR check: diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 0d92a269c5fa..f92c3695bfeb 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3244,6 +3244,12 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) u8 shadow_root_level = mmu->shadow_root_level; hpa_t root; unsigned i; + int r; + + write_lock(&vcpu->kvm->mmu_lock); + r = make_mmu_pages_available(vcpu); + if (r < 0) + goto out_unlock; if (is_tdp_mmu_enabled(vcpu->kvm)) { root = kvm_tdp_mmu_get_vcpu_root_hpa(vcpu); @@ -3266,13 +3272,16 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) mmu->root_hpa = __pa(mmu->pae_root); } else { WARN_ONCE(1, "Bad TDP root level = %d\n", shadow_root_level); - return -EIO; + r = -EIO; } +out_unlock: + write_unlock(&vcpu->kvm->mmu_lock); + /* root_pgd is ignored for direct MMUs. */ mmu->root_pgd = 0; - return 0; + return r; } static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) @@ -3282,6 +3291,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) gfn_t root_gfn, root_pgd; hpa_t root; int i; + int r; root_pgd = mmu->get_guest_pgd(vcpu); root_gfn = root_pgd >> PAGE_SHIFT; @@ -3300,6 +3310,11 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) } } + write_lock(&vcpu->kvm->mmu_lock); + r = make_mmu_pages_available(vcpu); + if (r < 0) + goto out_unlock; + /* * Do we shadow a long mode page table? If so we need to * write-protect the guests page table root. @@ -3308,7 +3323,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) root = mmu_alloc_root(vcpu, root_gfn, 0, mmu->shadow_root_level, false); mmu->root_hpa = root; - goto set_root_pgd; + goto out_unlock; } if (WARN_ON_ONCE(!mmu->pae_root)) @@ -3350,7 +3365,8 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) else mmu->root_hpa = __pa(mmu->pae_root); -set_root_pgd: +out_unlock: + write_unlock(&vcpu->kvm->mmu_lock); mmu->root_pgd = root_pgd; return 0; @@ -4852,14 +4868,10 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu) r = mmu_alloc_special_roots(vcpu); if (r) goto out; - write_lock(&vcpu->kvm->mmu_lock); - if (make_mmu_pages_available(vcpu)) - r = -ENOSPC; - else if (vcpu->arch.mmu->direct_map) + if (vcpu->arch.mmu->direct_map) r = mmu_alloc_direct_roots(vcpu); else r = mmu_alloc_shadow_roots(vcpu); - write_unlock(&vcpu->kvm->mmu_lock); if (r) goto out; Paolo