KVM: PPC: Add @offset to kvmppc_spapr_tce_table

This enables userspace view of TCE tables to start from non-zero offset
on a bus. This will be used for huge DMA windows.

This only changes the internal structure, the user interface needs to
change in order to use an offset.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/include/asm/kvm_host.h

@@ -184,6 +184,7 @@ struct kvmppc_spapr_tce_table {
 	u64 liobn;
 	struct rcu_head rcu;
 	u32 page_shift;
+	u64 offset;		/* in pages */
 	u64 size;		/* window size in pages */
 	struct page *pages[0];
 };

arch/powerpc/kvm/book3s_64_vio_hv.c

@@ -75,7 +75,9 @@ long kvmppc_ioba_validate(struct kvmppc_spapr_tce_table *stt,
 	unsigned long mask = (1ULL << stt->page_shift) - 1;
 	unsigned long idx = ioba >> stt->page_shift;
 
-	if ((ioba & mask) || (idx + npages > stt->size) || (idx + npages < idx))
+	if ((ioba & mask) || (idx < stt->offset) ||
+			(idx - stt->offset + npages > stt->size) ||
+			(idx + npages < idx))
 		return H_PARAMETER;
 
 	return H_SUCCESS;
@@ -147,6 +149,7 @@ void kvmppc_tce_put(struct kvmppc_spapr_tce_table *stt,
 	struct page *page;
 	u64 *tbl;
 
+	idx -= stt->offset;
 	page = stt->pages[idx / TCES_PER_PAGE];
 	tbl = kvmppc_page_address(page);
 
@@ -335,7 +338,7 @@ long kvmppc_h_get_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
 	if (ret != H_SUCCESS)
 		return ret;
 
-	idx = ioba >> stt->page_shift;
+	idx = (ioba >> stt->page_shift) - stt->offset;
 	page = stt->pages[idx / TCES_PER_PAGE];
 	tbl = (u64 *)page_address(page);