Host-guest event notification via configured interrupt vector is useful
in cases where a guest makes an asynchronous request and needs a
callback from the host to indicate the completion or to let the host
notify the guest about events like device removal. One usage example is,
callback requirement of GetQuote asynchronous hypercall.

In TDX guest, SetupEventNotifyInterrupt hypercall can be used by the
guest to specify which interrupt vector to use as an event-notify
vector to the VMM. Details about the SetupEventNotifyInterrupt
hypercall can be found in TDX Guest-Host Communication Interface
(GHCI) Specification, sec 3.5 "VP.VMCALL<SetupEventNotifyInterrupt>".
Add a tdx_hcall_set_notify_intr() helper function to implement the
SetupEventNotifyInterrupt hypercall.

Reserve 0xec IRQ vector address for TDX guest to receive the event
completion notification from VMM. Also add related IDT handler to
process the notification event.

Add support to track the notification event status via
/proc/interrupts.

Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Wander Lairson Costa <wander@redhat.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
 arch/x86/coco/tdx/tdx.c            | 73 ++++++++++++++++++++++++++++++
 arch/x86/include/asm/hardirq.h     |  3 ++
 arch/x86/include/asm/idtentry.h    |  4 ++
 arch/x86/include/asm/irq_vectors.h |  7 ++-
 arch/x86/include/asm/tdx.h         |  4 ++
 arch/x86/kernel/irq.c              |  7 +++
 6 files changed, 97 insertions(+), 1 deletion(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 03deb4d6920d..b49211994864 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -11,6 +11,10 @@
 #include <asm/insn.h>
 #include <asm/insn-eval.h>
 #include <asm/pgtable.h>
+#include <asm/apic.h>
+#include <asm/idtentry.h>
+#include <asm/irq_regs.h>
+#include <asm/desc.h>
 
 /* TDX module Call Leaf IDs */
 #define TDX_GET_INFO			1
@@ -19,6 +23,7 @@
 
 /* TDX hypercall Leaf IDs */
 #define TDVMCALL_MAP_GPA		0x10001
+#define TDVMCALL_SETUP_NOTIFY_INTR	0x10004
 
 /* MMIO direction */
 #define EPT_READ	0
@@ -34,6 +39,28 @@
 #define VE_GET_PORT_NUM(e)	((e) >> 16)
 #define VE_IS_IO_STRING(e)	((e) & BIT(4))
 
+/*
+ * Handler used to report notifications about
+ * TDX_GUEST_EVENT_NOTIFY_VECTOR IRQ. Currently it will be
+ * used only by the attestation driver. So, race condition
+ * with read/write operation is not considered.
+ */
+static void (*tdx_event_notify_handler)(void);
+
+/* Helper function to register tdx_event_notify_handler */
+void tdx_setup_ev_notify_handler(void (*handler)(void))
+{
+	tdx_event_notify_handler = handler;
+}
+EXPORT_SYMBOL_GPL(tdx_setup_ev_notify_handler);
+
+/* Helper function to unregister tdx_event_notify_handler */
+void tdx_remove_ev_notify_handler(void)
+{
+	tdx_event_notify_handler = NULL;
+}
+EXPORT_SYMBOL_GPL(tdx_remove_ev_notify_handler);
+
 /*
  * Wrapper for standard use of __tdx_hypercall with no output aside from
  * return code.
@@ -98,6 +125,46 @@ static inline void tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
 		panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
 }
 
+/* TDX guest event notification handler */
+DEFINE_IDTENTRY_SYSVEC(sysvec_tdx_event_notify)
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+
+	inc_irq_stat(irq_tdx_event_notify_count);
+
+	if (tdx_event_notify_handler)
+		tdx_event_notify_handler();
+
+	ack_APIC_irq();
+
+	set_irq_regs(old_regs);
+}
+
+/*
+ * tdx_hcall_set_notify_intr() - Setup Event Notify Interrupt Vector.
+ *
+ * @vector: Vector address to be used for notification.
+ *
+ * return 0 on success or failure error number.
+ */
+static long tdx_hcall_set_notify_intr(u8 vector)
+{
+	/* Minimum vector value allowed is 32 */
+	if (vector < 32)
+		return -EINVAL;
+
+	/*
+	 * Register callback vector address with VMM. More details
+	 * about the ABI can be found in TDX Guest-Host-Communication
+	 * Interface (GHCI), sec titled
+	 * "TDG.VP.VMCALL<SetupEventNotifyInterrupt>".
+	 */
+	if (_tdx_hypercall(TDVMCALL_SETUP_NOTIFY_INTR, vector, 0, 0, 0))
+		return -EIO;
+
+	return 0;
+}
+
 static u64 get_cc_mask(void)
 {
 	struct tdx_module_output out;
@@ -688,5 +755,11 @@ void __init tdx_early_init(void)
 	x86_platform.guest.enc_tlb_flush_required   = tdx_tlb_flush_required;
 	x86_platform.guest.enc_status_change_finish = tdx_enc_status_changed;
 
+	alloc_intr_gate(TDX_GUEST_EVENT_NOTIFY_VECTOR,
+			asm_sysvec_tdx_event_notify);
+
+	if (tdx_hcall_set_notify_intr(TDX_GUEST_EVENT_NOTIFY_VECTOR))
+		pr_warn("Setting event notification interrupt failed\n");
+
 	pr_info("Guest detected\n");
 }
diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
index 275e7fd20310..582deff56210 100644
--- a/arch/x86/include/asm/hardirq.h
+++ b/arch/x86/include/asm/hardirq.h
@@ -44,6 +44,9 @@ typedef struct {
 	unsigned int irq_hv_reenlightenment_count;
 	unsigned int hyperv_stimer0_count;
 #endif
+#if IS_ENABLED(CONFIG_INTEL_TDX_GUEST)
+	unsigned int irq_tdx_event_notify_count;
+#endif
 } ____cacheline_aligned irq_cpustat_t;
 
 DECLARE_PER_CPU_SHARED_ALIGNED(irq_cpustat_t, irq_stat);
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 72184b0b2219..655086dd940e 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -700,6 +700,10 @@ DECLARE_IDTENTRY_SYSVEC(HYPERVISOR_CALLBACK_VECTOR,	sysvec_xen_hvm_callback);
 DECLARE_IDTENTRY_SYSVEC(HYPERVISOR_CALLBACK_VECTOR,	sysvec_kvm_asyncpf_interrupt);
 #endif
 
+#if IS_ENABLED(CONFIG_INTEL_TDX_GUEST)
+DECLARE_IDTENTRY_SYSVEC(TDX_GUEST_EVENT_NOTIFY_VECTOR,	sysvec_tdx_event_notify);
+#endif
+
 #undef X86_TRAP_OTHER
 
 #endif
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 43dcb9284208..82ac0c0a34b1 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -104,7 +104,12 @@
 #define HYPERV_STIMER0_VECTOR		0xed
 #endif
 
-#define LOCAL_TIMER_VECTOR		0xec
+#if IS_ENABLED(CONFIG_INTEL_TDX_GUEST)
+/* Vector on which TDX Guest event notification is delivered */
+#define TDX_GUEST_EVENT_NOTIFY_VECTOR	0xec
+#endif
+
+#define LOCAL_TIMER_VECTOR		0xeb
 
 #define NR_VECTORS			 256
 
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 020c81a7c729..eb4db837cc44 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -67,6 +67,10 @@ void tdx_safe_halt(void);
 
 bool tdx_early_handle_ve(struct pt_regs *regs);
 
+void tdx_setup_ev_notify_handler(void (*handler)(void));
+
+void tdx_remove_ev_notify_handler(void);
+
 #else
 
 static inline void tdx_early_init(void) { };
diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 766ffe3ba313..a96ecd866723 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -181,6 +181,13 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 		seq_printf(p, "%10u ",
 			   irq_stats(j)->kvm_posted_intr_wakeup_ipis);
 	seq_puts(p, "  Posted-interrupt wakeup event\n");
+#endif
+#if IS_ENABLED(CONFIG_INTEL_TDX_GUEST)
+	seq_printf(p, "%*s: ", prec, "TGN");
+	for_each_online_cpu(j)
+		seq_printf(p, "%10u ",
+			   irq_stats(j)->irq_tdx_event_notify_count);
+	seq_puts(p, "  TDX Guest event notification\n");
 #endif
 	return 0;
 }
-- 
2.25.1

On Mon, May 23, 2022 at 09:05:14PM -0700, Kuppuswamy Sathyanarayanan wrote:
>  
> -#define LOCAL_TIMER_VECTOR		0xec
> +#if IS_ENABLED(CONFIG_INTEL_TDX_GUEST)
> +/* Vector on which TDX Guest event notification is delivered */
> +#define TDX_GUEST_EVENT_NOTIFY_VECTOR	0xec
> +#endif

We can simplify this a bit by removing the #if conditional without harm
to the code.

> +
> +#define LOCAL_TIMER_VECTOR		0xeb
>  
>  #define NR_VECTORS			 256
>

On 5/26/22 6:48 AM, Wander Lairson Costa wrote:
> On Mon, May 23, 2022 at 09:05:14PM -0700, Kuppuswamy Sathyanarayanan wrote:
>>   
>> -#define LOCAL_TIMER_VECTOR		0xec
>> +#if IS_ENABLED(CONFIG_INTEL_TDX_GUEST)
>> +/* Vector on which TDX Guest event notification is delivered */
>> +#define TDX_GUEST_EVENT_NOTIFY_VECTOR	0xec
>> +#endif
> 
> We can simplify this a bit by removing the #if conditional without harm
> to the code.

In non TDX environment, we don't initialize this vector. It is similar
to definitions related to HYPERV or KVM which also use #if defined. So
followed the same format.

> 
>> +
>> +#define LOCAL_TIMER_VECTOR		0xeb
>>   
>>   #define NR_VECTORS			 256
>>   
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

On Mon, 2022-05-23 at 21:05 -0700, Kuppuswamy Sathyanarayanan wrote:
> +/* Helper function to register tdx_event_notify_handler */
> +void tdx_setup_ev_notify_handler(void (*handler)(void))
> +{
> +	tdx_event_notify_handler = handler;
> +}
> +EXPORT_SYMBOL_GPL(tdx_setup_ev_notify_handler);
> +
> +/* Helper function to unregister tdx_event_notify_handler */
> +void tdx_remove_ev_notify_handler(void)
> +{
> +	tdx_event_notify_handler = NULL;
> +}
> +EXPORT_SYMBOL_GPL(tdx_remove_ev_notify_handler);

I don't think you need to export the two symbols now.

-- 
Thanks,
-Kai

Hi Kai,

On 5/23/22 11:40 PM, Kai Huang wrote:
>> +/* Helper function to register tdx_event_notify_handler */
>> +void tdx_setup_ev_notify_handler(void (*handler)(void))
>> +{
>> +	tdx_event_notify_handler = handler;
>> +}
>> +EXPORT_SYMBOL_GPL(tdx_setup_ev_notify_handler);
>> +
>> +/* Helper function to unregister tdx_event_notify_handler */
>> +void tdx_remove_ev_notify_handler(void)
>> +{
>> +	tdx_event_notify_handler = NULL;
>> +}
>> +EXPORT_SYMBOL_GPL(tdx_remove_ev_notify_handler);
> I don't think you need to export the two symbols now.

Agree. I will remove it.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer