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Mon, 27 Oct 2025 17:37:05 -0700 (PDT) Date: Mon, 27 Oct 2025 17:37:03 -0700 In-Reply-To: <55461c549803e08db97528127c29e092c597adc5.camel@intel.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list Mime-Version: 1.0 References: <20251017003244.186495-1-seanjc@google.com> <20251017003244.186495-25-seanjc@google.com> <55461c549803e08db97528127c29e092c597adc5.camel@intel.com> Message-ID: Subject: Re: [PATCH v3 24/25] KVM: TDX: Guard VM state transitions with "all" the locks From: Sean Christopherson To: Kai Huang Cc: "chenhuacai@kernel.org" , "frankja@linux.ibm.com" , "maz@kernel.org" , "borntraeger@linux.ibm.com" , "pjw@kernel.org" , "aou@eecs.berkeley.edu" , "kas@kernel.org" , "maobibo@loongson.cn" , "pbonzini@redhat.com" , "maddy@linux.ibm.com" , "palmer@dabbelt.com" , "imbrenda@linux.ibm.com" , "zhaotianrui@loongson.cn" , "anup@brainfault.org" , "oliver.upton@linux.dev" , "kvm@vger.kernel.org" , "linux-coco@lists.linux.dev" , Yan Y Zhao , "michael.roth@amd.com" , "linux-kernel@vger.kernel.org" , Ira Weiny , "loongarch@lists.linux.dev" , "binbin.wu@linux.intel.com" , "ackerleytng@google.com" , "kvmarm@lists.linux.dev" , "kvm-riscv@lists.infradead.org" , Vishal Annapurve , "linuxppc-dev@lists.ozlabs.org" , Rick P Edgecombe , "linux-mips@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-riscv@lists.infradead.org" , "x86@kernel.org" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Tue, Oct 28, 2025, Kai Huang wrote: > On Thu, 2025-10-16 at 17:32 -0700, Sean Christopherson wrote: > > @@ -2781,8 +2827,6 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *ar= gp) > > =C2=A0 if (r) > > =C2=A0 return r; > > =C2=A0 > > - guard(mutex)(&kvm->lock); > > - > > =C2=A0 switch (tdx_cmd.id) { > > =C2=A0 case KVM_TDX_CAPABILITIES: > > =C2=A0 r =3D tdx_get_capabilities(&tdx_cmd); >=20 > IIRC, this patch removes grabbing the kvm->lock in tdx_vm_ioctl() but onl= y > adds the "big hammer" to tdx_td_init() and tdx_td_finalize(), so the > tdx_get_capabilities() lost holding the kvm->lock. Ooh, yeah, nice catch, that is indeed silly and unnecessary churn. > As replied earlier, I think we can just hold the "big hammer" in > tdx_vm_ioctl()? Actually, I think we can have our cake and eat it too. With this slotted i= n as a prep patch, the big hammer can land directly in tdx_vm_ioctl(), without a= ny change in functionality for KVM_TDX_CAPABILITIES. -- From: Sean Christopherson Date: Mon, 27 Oct 2025 17:32:34 -0700 Subject: [PATCH] KVM: TDX: Don't copy "cmd" back to userspace for KVM_TDX_CAPABILITIES Don't copy the kvm_tdx_cmd structure back to userspace when handling KVM_TDX_CAPABILITIES, as tdx_get_capabilities() doesn't modify hw_error or any other fields. Opportunistically hoist the call to tdx_get_capabilities() outside of the kvm->lock critical section, as getting the capabilities doesn't touch the VM in any way, e.g. doesn't even take @kvm. Suggested-by: Kai Huang Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/tdx.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 1642da9c1fa9..43c0c3f6a8c0 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -2807,12 +2807,12 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp= ) if (r) return r; =20 + if (tdx_cmd.id =3D=3D KVM_TDX_CAPABILITIES) + return tdx_get_capabilities(&tdx_cmd); + guard(mutex)(&kvm->lock); =20 switch (tdx_cmd.id) { - case KVM_TDX_CAPABILITIES: - r =3D tdx_get_capabilities(&tdx_cmd); - break; case KVM_TDX_INIT_VM: r =3D tdx_td_init(kvm, &tdx_cmd); break; base-commit: 672537233b8da2c29dca7154bf3a3211af7f6128 --