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

Sathyanarayanan Kuppuswamy
2022-07-14T00:47:05Z

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