Re: [patch 1/8] test: allow functions to execute on non-irq context remotely

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Mar 25, 2010 at 06:25:56PM +0200, Avi Kivity wrote:
> On 03/24/2010 11:24 PM, Marcelo Tosatti wrote:
> >Which allows code to execute on remote cpus while receiving interrupts.
> >
> >Also move late smp initialization to common code, and the smp loop
> >to C code.
> 
> 
> >+
> >+void smp_loop(void)
> >+{
> >+    void (*fn)(void *data);
> >+    void *data;
> >+
> >+    asm volatile ("hlt");
> 
> Racy.  The interrupt can happen before the hlt, which will kill the
> cpu.  

Why would it kill the cpu? Only miss the event AFAICS. See patch below.

> Needs to be
> 
>     cli
>     while not smp_function():
>         sti; hlt
>         cli
>     sti
>     smp_function()(smp_data())
> 
> Also need to make sure two on_cpu_noipi()s don't stomp on each other.

Only cpu0 requests this ATM, and the IPIs to set function/data are
protected by a spinlock which serializes between cpu0<->target.

Its responsability of the caller to synchronization with termination. 

Are you OK with this:



test: allow functions to execute on non-irq context remotely

Which allows code to execute on remote cpus while receiving interrupts.

Also move late smp initialization to common code, and the smp loop
to C code.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: qemu-kvm/kvm/user/test/lib/x86/smp.c
===================================================================
--- qemu-kvm.orig/kvm/user/test/lib/x86/smp.c
+++ qemu-kvm/kvm/user/test/lib/x86/smp.c
@@ -114,7 +114,7 @@ void on_cpu_async(int cpu, void (*functi
 }
 
 
-void smp_init(void)
+void smp_init_ids(void)
 {
     int i;
     void ipi_entry(void);
@@ -125,4 +125,70 @@ void smp_init(void)
     for (i = 1; i < cpu_count(); ++i)
         on_cpu(i, setup_smp_id, 0);
 
+   printf("detected %d cpus\n", cpu_count());
+}
+
+static void *smp_function(void)
+{
+    void *fn;
+
+    asm ("mov %%gs:8, %0" : "=r"(fn));
+    return fn;
+}
+
+static void setup_smp_function(void *data)
+{
+    asm ("mov %0, %%gs:8" : : "r"(data) : "memory");
+}
+
+static void *smp_data(void)
+{
+    void *fn;
+
+    asm ("mov %%gs:16, %0" : "=r"(fn));
+    return fn;
+}
+
+static void setup_smp_data(void *data)
+{
+    asm ("mov %0, %%gs:16" : : "r"(data) : "memory");
+}
+
+void on_cpu_noipi(int cpu, void (*function)(void *data), void *data)
+{
+    if (cpu == smp_id())
+        function(data);
+    else {
+        on_cpu(cpu, setup_smp_data, data);
+        on_cpu(cpu, setup_smp_function, function);
+    }
+}
+
+static void irq_disable(void)
+{
+    asm volatile("cli");
+}
+
+static void irq_enable(void)
+{
+    asm volatile("sti");
+}
+
+void smp_loop(void)
+{
+    void (*fn)(void *data);
+
+    irq_disable();
+    fn = smp_function();
+    if (fn) {
+        setup_smp_function(0);
+        irq_enable();
+        fn(smp_data());
+        irq_disable();
+    }
+
+    irq_enable();
+    asm volatile ("hlt");
+    irq_disable();
+
 }
Index: qemu-kvm/kvm/user/test/lib/x86/smp.h
===================================================================
--- qemu-kvm.orig/kvm/user/test/lib/x86/smp.h
+++ qemu-kvm/kvm/user/test/lib/x86/smp.h
@@ -5,12 +5,11 @@ struct spinlock {
     int v;
 };
 
-void smp_init(void);
-
 int cpu_count(void);
 int smp_id(void);
 void on_cpu(int cpu, void (*function)(void *data), void *data);
 void on_cpu_async(int cpu, void (*function)(void *data), void *data);
+void on_cpu_noipi(int cpu, void (*function)(void *data), void *data);
 void spin_lock(struct spinlock *lock);
 void spin_unlock(struct spinlock *lock);
 
Index: qemu-kvm/kvm/user/test/x86/cstart64.S
===================================================================
--- qemu-kvm.orig/kvm/user/test/x86/cstart64.S
+++ qemu-kvm/kvm/user/test/x86/cstart64.S
@@ -165,7 +165,7 @@ ap_start64:
 	nop
 	lock incw cpu_online_count
 
-1:	hlt
+1:	call smp_loop
 	jmp 1b
 
 start64:
@@ -174,6 +174,7 @@ start64:
 	call enable_apic
 	call smp_init
 	call enable_x2apic
+	call smp_init_ids
 	call main
 	mov %eax, %edi
 	call exit
Index: qemu-kvm/kvm/user/test/x86/smptest.c
===================================================================
--- qemu-kvm.orig/kvm/user/test/x86/smptest.c
+++ qemu-kvm/kvm/user/test/x86/smptest.c
@@ -15,8 +15,6 @@ int main()
     int ncpus;
     int i;
 
-    smp_init();
-
     ncpus = cpu_count();
     printf("found %d cpus\n", ncpus);
     for (i = 0; i < ncpus; ++i)
Index: qemu-kvm/kvm/user/test/x86/vmexit.c
===================================================================
--- qemu-kvm.orig/kvm/user/test/x86/vmexit.c
+++ qemu-kvm/kvm/user/test/x86/vmexit.c
@@ -155,8 +155,6 @@ int main(void)
 {
 	int i;
 
-	smp_init();
-
 	for (i = 0; i < ARRAY_SIZE(tests); ++i)
 		do_test(&tests[i]);