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Sat, 17 May 2025 05:36:01 -0700 (PDT) Received: from [192.168.21.214] ([69.164.134.123]) by smtp.googlemail.com with ESMTPSA id 6a1803df08f44-6f8b08afb37sm25011526d6.49.2025.05.17.05.36.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 17 May 2025 05:36:00 -0700 (PDT) Message-ID: <219b6bd5-9afe-4d1c-aaab-03e5c580ce5c@redhat.com> Date: Sat, 17 May 2025 14:35:59 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] KVM: x86: Use kvzalloc() to allocate VM struct To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Vipin Sharma References: <20250516215422.2550669-1-seanjc@google.com> <20250516215422.2550669-3-seanjc@google.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: <20250516215422.2550669-3-seanjc@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/16/25 23:54, Sean Christopherson wrote: > Allocate VM structs via kvzalloc(), i.e. try to use a contiguous physical > allocation before falling back to __vmalloc(), to avoid the overhead of > establishing the virtual mappings. For non-debug builds, The SVM and VMX > (and TDX) structures are now just below 7000 bytes in the worst case > scenario (see below), i.e. are order-1 allocations, and will likely remain > that way for quite some time. > > Add compile-time assertions in vendor code to ensure the size of the > structures, sans the memslos hash tables, are order-0 allocations, i.e. > are less than 4KiB. There's nothing fundamentally wrong with a larger > kvm_{svm,vmx,tdx} size, but given that the size of the structure (without > the memslots hash tables) is below 2KiB after 18+ years of existence, > more than doubling the size would be quite notable. > > Add sanity checks on the memslot hash table sizes, partly to ensure they > aren't resized without accounting for the impact on VM structure size, and > partly to document that the majority of the size of VM structures comes > from the memslots. > > Signed-off-by: Sean Christopherson > --- > arch/x86/include/asm/kvm_host.h | 2 +- > arch/x86/kvm/svm/svm.c | 2 ++ > arch/x86/kvm/vmx/main.c | 2 ++ > arch/x86/kvm/vmx/vmx.c | 2 ++ > arch/x86/kvm/x86.h | 22 ++++++++++++++++++++++ > 5 files changed, 29 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 9667d6b929ee..3a985825a945 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1961,7 +1961,7 @@ void kvm_x86_vendor_exit(void); > #define __KVM_HAVE_ARCH_VM_ALLOC > static inline struct kvm *kvm_arch_alloc_vm(void) > { > - return __vmalloc(kvm_x86_ops.vm_size, GFP_KERNEL_ACCOUNT | __GFP_ZERO); > + return kvzalloc(kvm_x86_ops.vm_size, GFP_KERNEL_ACCOUNT); > } > > #define __KVM_HAVE_ARCH_VM_FREE > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 0ad1a6d4fb6d..d13e475c3407 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -5675,6 +5675,8 @@ static int __init svm_init(void) > { > int r; > > + KVM_SANITY_CHECK_VM_STRUCT_SIZE(kvm_svm); > + > __unused_size_checks(); > > if (!kvm_is_svm_supported()) > diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c > index d1e02e567b57..e18dfada2e90 100644 > --- a/arch/x86/kvm/vmx/main.c > +++ b/arch/x86/kvm/vmx/main.c > @@ -64,6 +64,8 @@ static __init int vt_hardware_setup(void) > vt_x86_ops.protected_apic_has_interrupt = tdx_protected_apic_has_interrupt; > } > > + KVM_SANITY_CHECK_VM_STRUCT_SIZE(kvm_tdx); I would put either both or no checks in main.c. Or if you use static_assert, you can also place the macro invocation close to the struct definition. Paolo > + */ > +#define KVM_SANITY_CHECK_VM_STRUCT_SIZE(x) \ > +do { \ > + BUILD_BUG_ON(get_order(sizeof(struct x) - SIZE_OF_MEMSLOTS_HASHTABLE) && \ > + !IS_ENABLED(CONFIG_DEBUG_KERNEL) && !IS_ENABLED(CONFIG_KASAN)); \ > + BUILD_BUG_ON(get_order(sizeof(struct x)) < 2 && \ > + !IS_ENABLED(CONFIG_DEBUG_KERNEL) && !IS_ENABLED(CONFIG_KASAN)); \ > +} while (0) > #define KVM_NESTED_VMENTER_CONSISTENCY_CHECK(consistency_check) \ > ({ \ > bool failed = (consistency_check); \