Re: [RFC PATCH v3 5/6] kvm/ppc/mpic: in-kernel MPIC emulation

On 04/03/2013 05:07:30 PM, Scott Wood wrote:

On 04/03/2013 04:58:56 PM, Alexander Graf wrote:

quoted

=20
=20
Am 03.04.2013 um 23:38 schrieb Scott Wood [off-list ref]:
=20

quoted

On 04/03/2013 11:19:42 AM, Alexander Graf wrote:

quoted

On 03.04.2013, at 03:57, Scott Wood wrote:

quoted

+    switch (attr->group) {
+    case KVM_DEV_MPIC_GRP_MISC:
+        switch (attr->attr) {
+        case KVM_DEV_MPIC_BASE_ADDR:
+            mutex_lock(&opp->kvm->slots_lock);
+            attr64 =3D opp->reg_base;
+            mutex_unlock(&opp->kvm->slots_lock);
+
+            if (copy_to_user((u64 __user *)(long)attr->addr,
+                     &attr64, sizeof(u64)))

u64 is tricky with put_user on 32bit hosts, so here copy_to_user =20

makes sense

quoted

What are the issues with put_user?  It looks like it's supported =20

with a pair of "stw" instructions.
=20
Oh? Last time I tried to use get/put_user for one_reg it failed on =20
ppc32. So maybe the u64 support is new?

=20
Not new according to git -- though I haven't tried to use it yet; =20
maybe it's broken.

Yeah, it's broken. :-P

__get_user_size() looks OK, but __get_user_check/nocheck() goes through =20
an intermediary "unsigned long __gu_val".

There's a separate __get_user64_nocheck() that uses "long long", but no =20
"check" variant, no "put", and it's only available in 32-bit builds.  =20
And it's not used anywhere (barring ungreppable token-pasting magic).  =20
Sigh.

-Scott=