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LinuxKPI: Allow cdev_pager prefault handler to steal pages

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from other vm_objects. This workarounds "Page already inserted" panic
in vm_page_insert routine triggered on attempt to mmap file created
with shmem_file_setup call. After introduction of "GTT mmap
interface v4" a.k.a. MMAP_OFFSET, vm_objects allocated by these calls
may try to own intersected sets of pages that leads to the assertion.

Reviewed by:	kib
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D32090
This commit is contained in:
Vladimir Kondratyev 2021-09-29 23:14:05 +03:00
parent bd6d55adb4
commit 62ff0566c9
1 changed files with 27 additions and 0 deletions
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27
sys/compat/linuxkpi/common/src/linux_page.c
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@ -281,6 +281,7 @@ lkpi_vmf_insert_pfn_prot_locked(struct vm_area_struct *vma, unsigned long addr,
unsigned long pfn, pgprot_t prot)
{
vm_object_t vm_obj = vma->vm_obj;
vm_object_t tmp_obj;
vm_page_t page;
vm_pindex_t pindex;
@ -296,6 +297,32 @@ retry:
page = PHYS_TO_VM_PAGE(IDX_TO_OFF(pfn));
if (!vm_page_busy_acquire(page, VM_ALLOC_WAITFAIL))
goto retry;
if (page->object != NULL) {
tmp_obj = page->object;
vm_page_xunbusy(page);
VM_OBJECT_WUNLOCK(vm_obj);
VM_OBJECT_WLOCK(tmp_obj);
if (page->object == tmp_obj &&
vm_page_busy_acquire(page, VM_ALLOC_WAITFAIL)) {
KASSERT(page->object == tmp_obj,
("page has changed identity"));
KASSERT((page->oflags & VPO_UNMANAGED) == 0,
("page does not belong to shmem"));
vm_pager_page_unswapped(page);
if (pmap_page_is_mapped(page)) {
vm_page_xunbusy(page);
VM_OBJECT_WUNLOCK(tmp_obj);
printf("%s: page rename failed: page "
"is mapped\n", __func__);
VM_OBJECT_WLOCK(vm_obj);
return (VM_FAULT_NOPAGE);
}
vm_page_remove(page);
}
VM_OBJECT_WUNLOCK(tmp_obj);
VM_OBJECT_WLOCK(vm_obj);
goto retry;
}
if (vm_page_insert(page, vm_obj, pindex)) {
vm_page_xunbusy(page);
return (VM_FAULT_OOM);