On 17.10.23 г. 13:14 ч., Kai Huang wrote:
To enable TDX the kernel needs to initialize TDX from two perspectives: 1) Do a set of SEAMCALLs to initialize the TDX module to make it ready to create and run TDX guests; 2) Do the per-cpu initialization SEAMCALL on one logical cpu before the kernel wants to make any other SEAMCALLs on that cpu (including those involved during module initialization and running TDX guests). The TDX module can be initialized only once in its lifetime. Instead of always initializing it at boot time, this implementation chooses an "on demand" approach to initialize TDX until there is a real need (e.g when requested by KVM). This approach has below pros: 1) It avoids consuming the memory that must be allocated by kernel and given to the TDX module as metadata (~1/256th of the TDX-usable memory), and also saves the CPU cycles of initializing the TDX module (and the metadata) when TDX is not used at all. 2) The TDX module design allows it to be updated while the system is running. The update procedure shares quite a few steps with this "on demand" initialization mechanism. The hope is that much of "on demand" mechanism can be shared with a future "update" mechanism. A boot-time TDX module implementation would not be able to share much code with the update mechanism. 3) Making SEAMCALL requires VMX to be enabled. Currently, only the KVM code mucks with VMX enabling. If the TDX module were to be initialized separately from KVM (like at boot), the boot code would need to be taught how to muck with VMX enabling and KVM would need to be taught how to cope with that. Making KVM itself responsible for TDX initialization lets the rest of the kernel stay blissfully unaware of VMX. Similar to module initialization, also make the per-cpu initialization "on demand" as it also depends on VMX being enabled. Add two functions, tdx_enable() and tdx_cpu_enable(), to enable the TDX module and enable TDX on local cpu respectively. For now tdx_enable() is a placeholder. The TODO list will be pared down as functionality is added. Export both tdx_cpu_enable() and tdx_enable() for KVM use. In tdx_enable() 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 may be called concurrently by other kernel components in the future. The per-cpu initialization on each cpu can only be done once during the module's life time. Use a per-cpu variable to track its status to make sure it is only done once in tdx_cpu_enable(). Also, a SEAMCALL to do TDX module global initialization must be done once on any logical cpu before any per-cpu initialization SEAMCALL. Do it inside tdx_cpu_enable() too (if hasn't been done). tdx_enable() can potentially invoke SEAMCALLs on any online cpus. The per-cpu initialization must be done before those SEAMCALLs are invoked on some cpu. To keep things simple, in tdx_cpu_enable(), always do the per-cpu initialization regardless of whether the TDX module has been initialized or not. And in tdx_enable(), don't call tdx_cpu_enable() but assume the caller has disabled CPU hotplug, done VMXON and tdx_cpu_enable() on all online cpus before calling tdx_enable(). Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
With the latest explanation from Kai : Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
