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X-CSE-ConnectionGUID: B7+YwTXqS4+qC87bCfkP7w== X-CSE-MsgGUID: 4XDwc+dXSl64MnKUGK4LJA== X-IronPort-AV: E=McAfee;i="6800,10657,11647"; a="78764596" X-IronPort-AV: E=Sophos;i="6.21,161,1763452800"; d="scan'208";a="78764596" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Dec 2025 09:45:10 -0800 X-CSE-ConnectionGUID: Or1e/VJgQfSaNFH0PfJKfQ== X-CSE-MsgGUID: PfkgpOCCQOOjbC3je0dOgQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,161,1763452800"; d="scan'208";a="198066920" Received: from schen9-mobl4.amr.corp.intel.com (HELO [10.125.111.100]) ([10.125.111.100]) by orviesa006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Dec 2025 09:45:11 -0800 Message-ID: <90837ad5-c9a6-42da-a5a8-fcd2d870dac8@intel.com> Date: Fri, 19 Dec 2025 09:45:09 -0800 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/7] KVM: x86: Extract VMXON and EFER.SVME enablement to kernel To: Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Paolo Bonzini Cc: linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, Chao Gao , Dan Williams References: <20251206011054.494190-1-seanjc@google.com> <20251206011054.494190-3-seanjc@google.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/5/25 17:10, Sean Christopherson wrote: > Move the innermost VMXON and EFER.SVME management logic out of KVM and > into to core x86 so that TDX can force VMXON without having to rely on > KVM being loaded, e.g. to do SEAMCALLs during initialization. > > Implement a per-CPU refcounting scheme so that "users", e.g. KVM and the > future TDX code, can co-exist without pulling the rug out from under each > other. > > To avoid having to choose between SVM and VMX, simply refuse to enable > either if both are somehow supported. No known CPU supports both SVM and > VMX, and it's comically unlikely such a CPU will ever exist. Yeah, that's totally a "please share your drugs" moment, if it happens. > +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. ;) 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(). 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. 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.