On 9/23/2021 4:52 PM, Thomas Gleixner wrote:

On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote:

+/* UPID Notification control status */
+#define UPID_ON		0x0	/* Outstanding notification */
+#define UPID_SN		0x1	/* Suppressed notification */
Come on. This are bits in upid.status, right? So why can't the comment
above these defines says so and why can't the names not reflect that?

I'll fix this.

quoted

+struct uintr_upid_ctx {
+	struct uintr_upid *upid;
+	refcount_t refs;

Please use tabular format for struct members.

Will do.

quoted

+};
+
+struct uintr_receiver {
+	struct uintr_upid_ctx *upid_ctx;
+};

So we need a struct to wrap a pointer to another struct. Why?

The struct will have more members added later.  Should the wrapper be 
created then?

I didn't want to add members that are not used in this patch.

quoted

+inline bool uintr_arch_enabled(void)

What's this arch_enabled indirection for? Is this used anywhere in
non-architecture code?

I'll remove this indirection.

It is a remnant of some older code that had uintr_fd managed outside of 
the x86 code.

quoted

+{
+	return static_cpu_has(X86_FEATURE_UINTR);
+}
+
+static inline bool is_uintr_receiver(struct task_struct *t)
+{
+	return !!t->thread.ui_recv;
+}
+
+static inline u32 cpu_to_ndst(int cpu)
+{
+	u32 apicid = (u32)apic->cpu_present_to_apicid(cpu);
+
+	WARN_ON_ONCE(apicid == BAD_APICID);

Brilliant. If x2apic is not enabled then this case returns

I'll fix this.

quoted

+	if (!x2apic_enabled())
+		return (apicid << 8) & 0xFF00;

   (BAD_APICID << 8) & 0xFF00 == 0xFF ....

quoted

+int do_uintr_unregister_handler(void)
+{
+	struct task_struct *t = current;
+	struct fpu *fpu = &t->thread.fpu;
+	struct uintr_receiver *ui_recv;
+	u64 msr64;
+
+	if (!is_uintr_receiver(t))
+		return -EINVAL;
+
+	pr_debug("recv: Unregister handler and clear MSRs for task=%d\n",
+		 t->pid);
+
+	/*
+	 * TODO: Evaluate usage of fpregs_lock() and get_xsave_addr(). Bugs
+	 * have been reported recently for PASID and WRPKRU.

Again. Which bugs and why haven't they been evaluated before posting?

I apologize again. This comment is no longer valid.

quoted

+	 * UPID and ui_recv will be referenced during context switch. Need to
+	 * disable preemption while modifying the MSRs, UPID and ui_recv thread
+	 * struct.
+	 */
+	fpregs_lock();

And because you need to disable preemption you need to use
fpregs_lock(), right? That's not what fpregs_lock() is about.

Got it. I'll evaluate the use of fpregs_lock() at all places.

quoted

+		wrmsrl(MSR_IA32_UINTR_MISC, msr64);
+		wrmsrl(MSR_IA32_UINTR_PD, 0ULL);
+		wrmsrl(MSR_IA32_UINTR_RR, 0ULL);
+		wrmsrl(MSR_IA32_UINTR_STACKADJUST, 0ULL);
+		wrmsrl(MSR_IA32_UINTR_HANDLER, 0ULL);
+	} else {
+		struct uintr_state *p;
+
+		p = get_xsave_addr(&fpu->state.xsave, XFEATURE_UINTR);
+		if (p) {
+			p->handler = 0;
+			p->stack_adjust = 0;
+			p->upid_addr = 0;
+			p->uinv = 0;
+			p->uirr = 0;
+		}

So p == NULL is expected here?

I'll fix this and other usages of get_xsave_addr().

Thanks,

Sohil