@@ -429,9 +429,13 @@ void kvmppc_unmap_pte(struct kvm *kvm, pte_t *pte, unsigned long gpa,
* Callers are responsible for flushing the PWC.
*
* When page tables are being unmapped/freed as part of page fault path
- * (full == false), ptes are not expected. There is code to unmap them
- * and emit a warning if encountered, but there may already be data
- * corruption due to the unexpected mappings.
+ * (full == false), valid ptes are generally not expected; however, there
+ * is one situation where they arise, which is when dirty page logging is
+ * turned off for a memslot while the VM is running. The new memslot
+ * becomes visible to page faults before the memslot commit function
+ * gets to flush the memslot, which can lead to a 2MB page mapping being
+ * installed for a guest physical address where there are already 64kB
+ * (or 4kB) mappings (of sub-pages of the same 2MB page).
*/
static void kvmppc_unmap_free_pte(struct kvm *kvm, pte_t *pte, bool full,
unsigned int lpid)
@@ -445,7 +449,6 @@ static void kvmppc_unmap_free_pte(struct kvm *kvm, pte_t *pte, bool full,
for (it = 0; it < PTRS_PER_PTE; ++it, ++p) {
if (pte_val(*p) == 0)
continue;
- WARN_ON_ONCE(1);
kvmppc_unmap_pte(kvm, p,
pte_pfn(*p) << PAGE_SHIFT,
PAGE_SHIFT, NULL, lpid);
Although in general we do not expect valid PTEs to be found in kvmppc_create_pte when we are inserting a large page mapping, there is one situation where this can occur. That is when dirty page logging is turned off for a memslot while the VM is running. Because the new memslots are installed before the old memslot is flushed in kvmppc_core_commit_memory_region_hv(), there is a window where a hypervisor page fault can try to install a 2MB (or 1GB) page where there are already small page mappings which were installed while dirty page logging was enabled and which have not yet been flushed. Since we have a situation where valid PTEs can legitimately be found by kvmppc_unmap_free_pte, and which can be triggered by userspace, just remove the WARN_ON_ONCE, since it is undesirable to have userspace able to trigger a kernel warning. Signed-off-by: Paul Mackerras <paulus@ozlabs.org> --- arch/powerpc/kvm/book3s_64_mmu_radix.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)