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

Marcelo Tosatti
2010-03-25T18:08:35Z

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]);