Re: [PATCH] kvm-userspace: fix memslot assignment

[Christian Borntraeger <borntraeger@de.ibm.com>]

Am Donnerstag, 31. Juli 2008 schrieb Avi Kivity:
> > +#if defined(__x86_64__) || defined(__i386__)
> > +#if defined(KVM_CAP_SET_TSS_ADDR)
> > +	if (ioctl(kvm->fd, KVM_CHECK_EXTENSION, KVM_CAP_SET_TSS_ADDR) > 0)
> >   
> 
> Should be <= here?

yes. But with the wrapper you suggest below its again >.

> 
> > +		i++;
> > +#else
> > +	i++;
> > +#endif
> > +#endif
> >   
> 
> Suggest a helper, kvm_supports_set_tss_addr(), to reduce further 
> braindamage.

Something like that? But then I get the following warning on non-x86:
libkvm.c:77: warning: 'kvm_supports_set_tss_addr' defined but not used

Should I mask the wrapper with config x86 as well?


---
 libkvm.c |   32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

Index: libkvm/libkvm.c
===================================================================
--- libkvm.orig/libkvm.c
+++ libkvm/libkvm.c
@@ -73,27 +73,29 @@ void init_slots(void)
 		slots[i].len = 0;
 }
 
+static int kvm_supports_set_tss_addr(kvm_context_t kvm)
+{
+#if defined(KVM_CAP_SET_TSS_ADDR)
+	if (ioctl(kvm->fd, KVM_CHECK_EXTENSION, KVM_CAP_SET_TSS_ADDR) > 0)
+		return 1;
+#endif
+	return 0;
+}
+
 int get_free_slot(kvm_context_t kvm)
 {
 	int i;
-	int tss_ext;
-
-#if defined(KVM_CAP_SET_TSS_ADDR) && !defined(__s390__)
-	tss_ext = ioctl(kvm->fd, KVM_CHECK_EXTENSION, KVM_CAP_SET_TSS_ADDR);
-#else
-	tss_ext = 0;
-#endif
 
 	/*
-	 * on older kernels where the set tss ioctl is not supprted we must save
-	 * slot 0 to hold the extended memory, as the vmx will use the last 3
-	 * pages of this slot.
+	 * on older x86 kernels where the set tss ioctl is not supported we
+	 * must save slot 0 to hold the extended memory, as the vmx will
+	 * use the last 3 pages of this slot.
 	 */
-	if (tss_ext > 0)
-		i = 0;
-	else
-		i = 1;
-
+#if defined(__x86_64__) || defined(__i386__)
+	i = !kvm_supports_set_tss_addr(kvm);
+#else
+	i = 0;
+#endif
 	for (; i < KVM_MAX_NUM_MEM_REGIONS; ++i)
 		if (!slots[i].len)
 			return i;