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

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

Am Donnerstag, 31. Juli 2008 schrieb Avi Kivity:
> If we rename the helper, kvm_wants_special_memslot_0() (reversing the 
> meaning), we can have non-x86 return 0, x86 with KVM_CAP_SET_TSS_ADDR 
> return  0, and otherwise return 1.  No ifdefs outside the helper this way.
Having two ifdefs is not going to be very pretty, but here is the latest
version:


ppc, ia64 and s390 can start with slot 0 and it is not a special slot.
On x86 slot 0 is special, if
* KVM_CAP_SET_TSS_ADDR is not available
or
* The ioctl VM_CAP_SET_TSS_ADDR returns <=0
Lets introduce a helper that checks if we need a special memslot.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

---
 libkvm.c |   35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

Index: libkvm/libkvm.c
===================================================================
--- libkvm.orig/libkvm.c
+++ libkvm/libkvm.c
@@ -73,26 +73,29 @@ void init_slots(void)
 		slots[i].len = 0;
 }
 
-int get_free_slot(kvm_context_t kvm)
+static int kvm_wants_special_memslot_0(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);
+#if !defined(__x86_64__) && !defined(__i386__)
+	return 0;
 #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(KVM_CAP_SET_TSS_ADDR)
+	if (ioctl(kvm->fd, KVM_CHECK_EXTENSION, KVM_CAP_SET_TSS_ADDR) > 0)
+		return 0;
+#endif
+	return 1;
+#endif
+}
+
+int get_free_slot(kvm_context_t kvm)
+{
+	int i;
+
+	i = kvm_wants_special_memslot_0(kvm);
 
 	for (; i < KVM_MAX_NUM_MEM_REGIONS; ++i)
 		if (!slots[i].len)