One way of supporting a guard page below kstack: allocate kstacks in

procinit() and map them high up (below TRAMPOLNE) with an empty
mapping below each stack.  Never free a kernel stack.

Another way would be to allocate and map them dynamically, but then we
need to reload page table when switching processes in scheduler()
and/or have a kernel pagetable per proc (if we want k->stack to be the
same virtual address in each process).

One gotcha: kernel addresses are not equal to physical addresses for
stack addresses.  A stack address must be translated if we need its
physical address (e.g., virtio passes a stack address to the disk).

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/virtio_disk.c b/kernel/virtio_disk.c
index 1a29ce7..6620037 100644
--- a/kernel/virtio_disk.c
+++ b/kernel/virtio_disk.c
@@ -199,7 +199,7 @@ virtio_disk_rw(struct buf *b)
   buf0.reserved = 0;
   buf0.sector = sector;
 
-  desc[idx[0]].addr = (uint64) &buf0;
+  desc[idx[0]].addr = (uint64) kernelpa((uint64) &buf0);
   desc[idx[0]].len = sizeof(buf0);
   desc[idx[0]].flags = VRING_DESC_F_NEXT;
   desc[idx[0]].next = idx[1];