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AJvYcCXlwl5RexHOE0RPdeZDD77iWFMvPCsp+i43QvJGobdTUEcf2vOgRRRjrEmqqsmPQNVRat1AitFWWIlYsLE=@vger.kernel.org X-Gm-Message-State: AOJu0YzVXZHXFo5UPs6UbtXJDHbPyNiJp03wAZY87KqMuzDo9P5pQUez yZSz+GJ9F2Hp9fxNgxHDNLYVgmqpSeORi5D8OeTd0cB6VhUaSisIrQ9fBGKzzvzbOjETkkzfJKs GkDUHXw== X-Google-Smtp-Source: AGHT+IGvd+XfHbhthTzkZFT+g/Baf1kbE8bktfWBbuaDWMKWgA1wLhpc2ZL5cUoEo9s4pLMCpJWmqB/MBhg= X-Received: from pjqv1.prod.google.com ([2002:a17:90a:af01:b0:349:8a6d:dfd1]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2d50:b0:343:43bf:bcd7 with SMTP id 98e67ed59e1d1-34e90de0291mr3447619a91.13.1766169330430; Fri, 19 Dec 2025 10:35:30 -0800 (PST) Date: Fri, 19 Dec 2025 10:35:28 -0800 In-Reply-To: <90837ad5-c9a6-42da-a5a8-fcd2d870dac8@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251206011054.494190-1-seanjc@google.com> <20251206011054.494190-3-seanjc@google.com> <90837ad5-c9a6-42da-a5a8-fcd2d870dac8@intel.com> Message-ID: Subject: Re: [PATCH v2 2/7] KVM: x86: Extract VMXON and EFER.SVME enablement to kernel From: Sean Christopherson To: Dave Hansen 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, Chao Gao , Dan Williams Content-Type: text/plain; charset="us-ascii" On Fri, Dec 19, 2025, Dave Hansen wrote: > On 12/5/25 17:10, Sean Christopherson wrote: > > +static int x86_vmx_get_cpu(void) > > +{ > > + int r; > > + > > + if (cr4_read_shadow() & X86_CR4_VMXE) > > + return -EBUSY; > > + > > + intel_pt_handle_vmx(1); > > + > > + r = x86_virt_cpu_vmxon(); > > + if (r) { > > + intel_pt_handle_vmx(0); > > + return r; > > + } > > + > > + return 0; > > +} > ...> +#define x86_virt_call(fn) \ > > +({ \ > > + int __r; \ > > + \ > > + if (IS_ENABLED(CONFIG_KVM_INTEL) && \ > > + cpu_feature_enabled(X86_FEATURE_VMX)) \ > > + __r = x86_vmx_##fn(); \ > > + else if (IS_ENABLED(CONFIG_KVM_AMD) && \ > > + cpu_feature_enabled(X86_FEATURE_SVM)) \ > > + __r = x86_svm_##fn(); \ > > + else \ > > + __r = -EOPNOTSUPP; \ > > + \ > > + __r; \ > > +}) > > I'm not a super big fan of this. I know you KVM folks love your macros > and wrapping function calls in them because you hate grep. ;) Heh, kvm_x86_call() exists _because_ I like grep and search functionality. The number of times I couldn't find something because I was searching for full words and forgot about the kvm_x86_ prefix... > I don't like a foo_get_cpu() call having such fundamentally different > semantics than good old get_cpu() itself. *Especially* when the calls > look like: > > r = x86_virt_call(get_cpu); > > and get_cpu() itself it not invovled one bit. This 100% looks like it's > some kind of virt-specific call for get_cpu(). > > I think it's probably OK to make this get_hw_ref() or inc_hw_ref() or > something to get it away from getting confused with get_cpu(). Oof, yeah, didn't think about a collision with {get,put}_cpu(). How about x86_virt_{get,put}_ref()? I like how the callers read, e.g. "get a reference to VMX or SVM": x86_virt_get_ref(X86_FEATURE_VMX); x86_virt_put_ref(X86_FEATURE_VMX); x86_virt_get_ref(X86_FEATURE_SVM); x86_virt_put_ref(X86_FEATURE_SVM); > IMNHO, the macro magic is overkill. A couple of global function pointers > would probably be fine because none of this code is even remotely > performance sensitive. A couple static_call()s would be fine too because > those at least make it blatantly obvious that the thing being called is > variable. A good ol' ops structure would also make things obvious, but > are probably also overkill-adjecent for this. Agreed. I'm not even entirely sure why I took this approach. I suspect I carried over the basic concept from code that wanted to run before wiring up function pointers, and never revisited the implementation once the dust settled. I haven't tested yet, but I've got this: struct x86_virt_ops { int feature; int (*enable_virtualization_cpu)(void); int (*disable_virtualization_cpu)(void); void (*emergency_disable_virtualization_cpu)(void); }; static struct x86_virt_ops virt_ops __ro_after_init; and then usage like: int x86_virt_get_ref(int feat) { int r; if (!virt_ops.feature || virt_ops.feature != feat) return -EOPNOTSUPP; if (this_cpu_inc_return(virtualization_nr_users) > 1) return 0; r = virt_ops.enable_virtualization_cpu(); if (r) WARN_ON_ONCE(this_cpu_dec_return(virtualization_nr_users)); return r; } EXPORT_SYMBOL_GPL(x86_virt_get_ref); void x86_virt_put_ref(int feat) { if (WARN_ON_ONCE(!this_cpu_read(virtualization_nr_users)) || this_cpu_dec_return(virtualization_nr_users)) return; BUG_ON(virt_ops.disable_virtualization_cpu() && !virt_rebooting); } EXPORT_SYMBOL_GPL(x86_virt_put_ref); > P.S. In a perfect world, the renames would also be in their own patches, > but I think I can live with it as-is. Ya, I'll chunk the patch up.