A follow-up patch will add support for preemption in p2m_cache_flush_range.
Because of the complexity for the 2 loops, it would be necessary to add
preemption in both of them.
This can be avoided by merging the 2 loops together and still keeping
the code fairly simple to read and extend.
Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
---
Changes in v2:
- Patch added
---
xen/arch/arm/p2m.c | 52 +++++++++++++++++++++++++++++++++++++---------------
1 file changed, 37 insertions(+), 15 deletions(-)
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index c713226561..db22b53bfd 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1527,7 +1527,8 @@ int relinquish_p2m_mapping(struct domain *d)
int p2m_cache_flush_range(struct domain *d, gfn_t start, gfn_t end)
{
struct p2m_domain *p2m = p2m_get_hostp2m(d);
- gfn_t next_gfn;
+ gfn_t next_block_gfn;
+ mfn_t mfn = INVALID_MFN;
p2m_type_t t;
unsigned int order;
@@ -1542,24 +1543,45 @@ int p2m_cache_flush_range(struct domain *d, gfn_t start, gfn_t end)
start = gfn_max(start, p2m->lowest_mapped_gfn);
end = gfn_min(end, p2m->max_mapped_gfn);
- for ( ; gfn_x(start) < gfn_x(end); start = next_gfn )
- {
- mfn_t mfn = p2m_get_entry(p2m, start, &t, NULL, &order, NULL);
+ next_block_gfn = start;
- next_gfn = gfn_next_boundary(start, order);
-
- /* Skip hole and non-RAM page */
- if ( mfn_eq(mfn, INVALID_MFN) || !p2m_is_any_ram(t) )
- continue;
-
- /* XXX: Implement preemption */
- while ( gfn_x(start) < gfn_x(next_gfn) )
+ while ( gfn_x(start) < gfn_x(end) )
+ {
+ /*
+ * We want to flush page by page as:
+ * - it may not be possible to map the full block (can be up to 1GB)
+ * in Xen memory
+ * - we may want to do fine grain preemption as flushing multiple
+ * page in one go may take a long time
+ *
+ * As p2m_get_entry is able to return the size of the mapping
+ * in the p2m, it is pointless to execute it for each page.
+ *
+ * We can optimize it by tracking the gfn of the next
+ * block. So we will only call p2m_get_entry for each block (can
+ * be up to 1GB).
+ */
+ if ( gfn_eq(start, next_block_gfn) )
{
- flush_page_to_ram(mfn_x(mfn), false);
+ mfn = p2m_get_entry(p2m, start, &t, NULL, &order, NULL);
+ next_block_gfn = gfn_next_boundary(start, order);
- start = gfn_add(start, 1);
- mfn = mfn_add(mfn, 1);
+ /*
+ * The following regions can be skipped:
+ * - Hole
+ * - non-RAM
+ */
