On 18/11/2024 2:22 pm, Chao Gao wrote:
+static int tdx_online_cpu(unsigned int cpu)
+{
+ unsigned long flags;
+ int r;
+
+ /* Sanity check CPU is already in post-VMXON */
+ WARN_ON_ONCE(!(cr4_read_shadow() & X86_CR4_VMXE));
+
+ local_irq_save(flags);
+ r = tdx_cpu_enable();
+ local_irq_restore(flags);
The comment above tdx_cpu_enable() is outdated because now it may be called
from CPU hotplug rather than IPI function calls only.
Can we relax the assertion lockdep_assert_irqs_disabled() in tdx_cpu_enable()?
looks the requirement is just the enabling work won't be migrated and done to
another CPU.
We can but I don't want to do it now. We will need to revist both
tdx_cpu_enable() and tdx_enable() when we move VMXON out of KVM anyway.
I would like to focus on bringing KVM TDX support first and then to
revisit them together at that timeframe.
+
+ return r;
+}
+
+static void __do_tdx_cleanup(void)
+{
+ /*
+ * Once TDX module is initialized, it cannot be disabled and
+ * re-initialized again w/o runtime update (which isn't
+ * supported by kernel). Only need to remove the cpuhp here.
+ * The TDX host core code tracks TDX status and can handle
+ * 'multiple enabling' scenario.
+ */
+ WARN_ON_ONCE(!tdx_cpuhp_state);
+ cpuhp_remove_state_nocalls(tdx_cpuhp_state);
...
+ tdx_cpuhp_state = 0;
+}
+
+static int __init __do_tdx_bringup(void)
+{
+ int r;
+
+ /*
+ * TDX-specific cpuhp callback to call tdx_cpu_enable() on all
+ * online CPUs before calling tdx_enable(), and on any new
+ * going-online CPU to make sure it is ready for TDX guest.
+ */
+ r = cpuhp_setup_state_cpuslocked(CPUHP_AP_ONLINE_DYN,
+ "kvm/cpu/tdx:online",
+ tdx_online_cpu, NULL);
+ if (r < 0)
+ return r;
+
+ tdx_cpuhp_state = r;
+
+ r = tdx_enable();
+ if (r)
+ __do_tdx_cleanup();
this calls cpuhp_remove_state_nocalls(), which acquires cpu locks again,
causing a potential deadlock IIUC.
Dam.. I'll fix. Thanks for catching.
+
+ return r;
+}
+
+static bool __init kvm_can_support_tdx(void)
I think "static __init bool" is the preferred order. see
https://www.kernel.org/doc/html/latest/process/coding-style.html#function-prototypes
I think you are right, but IIUC we'd better to change all the existing
'static <ret_type> __init' to 'static __init <ret_type>' in KVM code.
I'd rather to keep the current way to make them aligned and we can
change them at once if needed in the future.
+{
+ return cpu_feature_enabled(X86_FEATURE_TDX_HOST_PLATFORM);
+}
+
+static int __init __tdx_bringup(void)
+{
+ int r;
+
+ /*
+ * Enabling TDX requires enabling hardware virtualization first,
+ * as making SEAMCALLs requires CPU being in post-VMXON state.
+ */
+ r = kvm_enable_virtualization();
+ if (r)
+ return r;
+
+ cpus_read_lock();
+ r = __do_tdx_bringup();
+ cpus_read_unlock();
+
+ if (r)
+ goto tdx_bringup_err;
+
+ /*
+ * Leave hardware virtualization enabled after TDX is enabled
+ * successfully. TDX CPU hotplug depends on this.
+ */
Shouldn't we make enable_tdx dependent on enable_virt_at_load? Otherwise, if
someone sets enable_tdx=1 and enable_virt_at_load=0, they will get hardware
virtualization enabled at load time while enable_virt_at_load still shows 0.
This behavior is a bit confusing to me.
I think a check against enable_virt_at_load in kvm_can_support_tdx() will work.
The call of kvm_enable_virtualization() here effectively moves
kvm_init_virtualization() out of kvm_init() when enable_tdx=1. I wonder if it
makes more sense to refactor out kvm_init_virtualization() for non-TDX cases
as well, i.e.,
vmx_init();
kvm_init_virtualization();
tdx_init();
kvm_init();
I'm not sure if this was ever discussed. To me, this approach is better because
TDX code needn't handle virtualization enabling stuff. It can simply check that
enable_virt_at_load=1, assume virtualization is enabled and needn't disable
virtualization on errors.
I think this was briefly discussed here:
https://lore.kernel.org/all/ZrrFgBmoywk7eZYC@xxxxxxxxxx/
The disadvantage of splitting out kvm_init_virtualization() is all other
ARCHs (all non-TDX cases actually) will need to explicitly call
kvm_init_virtualization() separately.
A bonus is that on non-TDX-capable systems, hardware virtualization won't be
toggled twice at KVM load time for no good reason.
I am fine with either way.
Sean, do you have any comments?
