Re: [PATCH v8 2/5] x86/tdx: Add TDX Guest event notify interrupt support

[Sathyanarayanan Kuppuswamy]

Hi Kai/Dave,

On 6/27/22 4:21 AM, Kai Huang wrote:
> On Sat, 2022-06-25 at 15:35 +1200, Yao, Jiewen wrote:
>> Thank you, Jun.
>>
>> Yes. I confirmed that we will include below change to GHCI.next spec.
>>
>> ================
>> 3.5 TDG.VP.VMCALL<SetupEventNotifyInterrupt>
>>
>> From: "The host VMM should use SEAMCALL [TDWRVPS] leaf to inject an interrupt at the requested-interrupt vector into the TD via the posted-interrupt descriptor. "
>>
>> To: "The host VMM should use SEAMCALL [TDWRVPS] leaf to inject an interrupt at the requested-interrupt vector into the TD VCPU that executed TDG.VP.VMCALL <SetupEventNotifyInterrupt> via the posted-interrupt descriptor. "
>>
> 
> Hi Sathy,
> 
> With this change, I don't think we should use system vector anymore.  Instead,
> we just need one non-migratable IRQ which has a fixed vector on a fixed cpu.
> 

Thanks. As suggested, I have attempted to allocate IRQ vector at runtime
using irq_domain_alloc_irqs() call. Vector is allocated from
"x86_vector_domain" as Kai suggested.

Since I am not well versed in this area, I would like expert comments on it.
Mainly for IRQ allocation logic in tdx_late_init(). I have tested this version using
QEMU and it works fine.


diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 928dcf7a20d9..dcc878546574 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -5,12 +5,16 @@
 #define pr_fmt(fmt)     "tdx: " fmt
 
 #include <linux/cpufeature.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/numa.h>
 #include <asm/coco.h>
 #include <asm/tdx.h>
 #include <asm/vmx.h>
 #include <asm/insn.h>
 #include <asm/insn-eval.h>
 #include <asm/pgtable.h>
+#include <asm/irqdomain.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 +39,26 @@
 #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;
+}
+
+/* Helper function to unregister tdx_event_notify_handler */
+void tdx_remove_ev_notify_handler(void)
+{
+       tdx_event_notify_handler = NULL;
+}
+
 /*
  * Wrapper for standard use of __tdx_hypercall with no output aside from
  * return code.
@@ -98,6 +123,31 @@ 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_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;
@@ -775,3 +825,52 @@ void __init tdx_early_init(void)
 
        pr_info("Guest detected\n");
 }
+
+static irqreturn_t tdx_ev_handler(int irq, void *dev_id)
+{
+       tdx_event_notify_handler();
+       return IRQ_HANDLED;
+}
+
+static int __init tdx_late_init(void)
+{
+        struct irq_alloc_info info;
+       struct irq_cfg *cfg;
+       int evirq, cpu;
+
+       if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+               return 0;
+
+       if (!x86_vector_domain) {
+               pr_err("x86 vector domain is NULL\n");
+               return 0;
+       }
+
+       init_irq_alloc_info(&info, NULL);
+
+       evirq = irq_domain_alloc_irqs(x86_vector_domain, 1, NUMA_NO_NODE, &info);
+
+       cpu = get_cpu();
+
+       irq_set_handler(evirq, handle_edge_irq);
+
+       /*
+        * Event notification vector will be delivered to the CPU
+        * in which TDVMCALL_SETUP_NOTIFY_INTR hypercall is requested.
+        * So set the IRQ affinity to the current CPU.
+        */
+       irq_set_affinity(evirq, cpumask_of(cpu));
+
+       if (request_irq(evirq, tdx_ev_handler, 0, "tdx_evirq", NULL))
+               pr_err("Request event IRQ failed\n");
+
+       cfg = irq_cfg(evirq);
+
+       if (tdx_hcall_set_notify_intr(cfg->vector))
+               pr_err("Setting event notification interrupt failed\n");
+
+       put_cpu();
+
+       return 0;
+}
+late_initcall(tdx_late_init);
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) { };


-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer