Hi Yanan,
On 2020-12-14 07:20, wangyanan (Y) wrote:
diff --git a/arch/arm64/kvm/hyp/pgtable.c
b/arch/arm64/kvm/hyp/pgtable.c
index a74a62283012..e3c6133567c4 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -45,6 +45,10 @@
#define KVM_PTE_LEAF_ATTR_HI_S2_XN BIT(54)
+#define KVM_PTE_LEAF_ATTR_S2_PERMS (KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | \
+ KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | \
+ KVM_PTE_LEAF_ATTR_HI_S2_XN)
+
struct kvm_pgtable_walk_data {
struct kvm_pgtable *pgt;
struct kvm_pgtable_walker *walker;
@@ -473,8 +477,13 @@ static bool stage2_map_walker_try_leaf(u64 addr,
u64 end, u32 level,
new = kvm_init_valid_leaf_pte(phys, data->attr, level);
if (kvm_pte_valid(old)) {
- /* Tolerate KVM recreating the exact same mapping. */
- if (old == new)
+ /*
+ * Skip updating the PTE with break-before-make if we
are trying
+ * to recreate the exact same mapping or only change
the access
+ * permissions. Actually, change of permissions will be
handled
+ * through the relax_perms path next time if necessary.
+ */
+ if (!((old ^ new) & (~KVM_PTE_LEAF_ATTR_S2_PERMS)))
goto out;
/* There's an existing different valid leaf entry, so
perform
I think there is a bit more work to do on this.
One obvious issue is that we currently flag a page as dirty before
handling
the fault. With an early exit, we end-up having spurious dirty pages.
It's not a big deal, but I'd rather mark the page dirty after the
mapping
or the permission update having been successful (at the moment, it
cannot
fails).
Thanks,
M.
--
Jazz is not dead. It just smells funny...