Merge tag 'kvm-s390-master-5.14-1' of git://git.kernel.org/pub/scm/linux/kernel/git...

[platform/kernel/linux-starfive.git] / virt / kvm / kvm_main.c

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3dcc2ab..f7445c3 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2175,6 +2175,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)
        return true;
 }
 
+static int kvm_try_get_pfn(kvm_pfn_t pfn)
+{
+       if (kvm_is_reserved_pfn(pfn))
+               return 1;
+       return get_page_unless_zero(pfn_to_page(pfn));
+}
+
 static int hva_to_pfn_remapped(struct vm_area_struct *vma,
                               unsigned long addr, bool *async,
                               bool write_fault, bool *writable,
@@ -2224,13 +2231,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
         * Whoever called remap_pfn_range is also going to call e.g.
         * unmap_mapping_range before the underlying pages are freed,
         * causing a call to our MMU notifier.
+        *
+        * Certain IO or PFNMAP mappings can be backed with valid
+        * struct pages, but be allocated without refcounting e.g.,
+        * tail pages of non-compound higher order allocations, which
+        * would then underflow the refcount when the caller does the
+        * required put_page. Don't allow those pages here.
         */ 
-       kvm_get_pfn(pfn);
+       if (!kvm_try_get_pfn(pfn))
+               r = -EFAULT;
 
 out:
        pte_unmap_unlock(ptep, ptl);
        *p_pfn = pfn;
-       return 0;
+
+       return r;
 }
 
 /*