Message-ID: <a44246e1-72de-4c9a-c602-dfc2f7df129b@intel.com>
Date:   Tue, 14 Feb 2023 09:23:40 -0800
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Subject: Re: [PATCH v9 04/18] x86/virt/tdx: Add skeleton to initialize TDX on
 demand
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To:     Peter Zijlstra <peterz@infradead.org>,
        Kai Huang <kai.huang@intel.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-mm@kvack.org, tglx@linutronix.de, seanjc@google.com,
        pbonzini@redhat.com, dan.j.williams@intel.com,
        rafael.j.wysocki@intel.com, kirill.shutemov@linux.intel.com,
        ying.huang@intel.com, reinette.chatre@intel.com,
        len.brown@intel.com, tony.luck@intel.com, ak@linux.intel.com,
        isaku.yamahata@intel.com, chao.gao@intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com, david@redhat.com,
        bagasdotme@gmail.com, sagis@google.com, imammedo@redhat.com
References: <cover.1676286526.git.kai.huang@intel.com>
 <eb565156d84e35a846a886025513a712f2ac2f83.1676286526.git.kai.huang@intel.com>
 <Y+uCtZ7itiNsbR4j@hirez.programming.kicks-ass.net>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <Y+uCtZ7itiNsbR4j@hirez.programming.kicks-ass.net>
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Precedence: bulk

On 2/14/23 04:46, Peter Zijlstra wrote:
> On Tue, Feb 14, 2023 at 12:59:11AM +1300, Kai Huang wrote:
>> Use a state machine protected by mutex to make sure the initialization
>> will only be done once, as tdx_enable() can be called multiple times
>> (i.e. KVM module can be reloaded) and be called concurrently by other
>> kernel components in the future.
> I still object to doing tdx_enable() at kvm module load.
> 
> kvm.ko gets loaded unconditionally on boot, even if I then never use
> kvm.
> 
> This stuff needs to be done when an actual VM is created, not before.

The actually implementation of this is hidden over in the KVM side of
this.  But, tdx_enable() and all of this jazz should not be called on
kvm.ko load.  It'll happen when the KVM tries to start the first TDX VM.

I think what Kai was thinking of was *this* sequence:

 1. insmod kvm.ko
 2. Start a TDX guest, tdx_enable() gets run
 3. rmmod kvm
 4. insmod kvm.ko (again)
 5. Start another TDX guest, run tdx_enable() (again)

The rmmod/insmod pair is what triggers the second call of tdx_enable().