During process startup, in xen_pgd_pin(), we pin PTE pages
but not PMD pages. If we then later map and unmap using an
otherwise unused PMD page, the unpin in release_pd() fails
because it wasn't previously pinned.
i.e. with this simple test case:
int fd = open("/dev/zero", O_RDONLY);
munmap(mmap((void *)0x40000000, 0x1000_LEN, PROT_READ, MAP_PRIVATE, fd, 0),
0x1000);
close(fd);
we currently get:
kernel BUG at arch/x86/xen/enlighten.c:678!
...
EIP is at xen_release_pt+0x79/0xa9
...
Call Trace:
[<c041da25>] ? __pmd_free_tlb+0x1a/0x75
[<c047a192>] ? free_pgd_range+0x1d2/0x2b5
[<c047a2f3>] ? free_pgtables+0x7e/0x93
[<c047b272>] ? unmap_region+0xb9/0xf5
[<c047c1bd>] ? do_munmap+0x193/0x1f5
[<c047c24f>] ? sys_munmap+0x30/0x3f
[<c0408cce>] ? syscall_call+0x7/0xb
=======================
and xen complains:
(XEN) mm.c:2241:d4 Mfn 1cc37 not pinned
Further details at:
https://bugzilla.redhat.com/436453
Signed-off-by: Mark McLoughlin <markmc@xxxxxxxxxx>
---
arch/x86/xen/enlighten.c | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 16e2f80..f16b056 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -689,8 +689,6 @@ static void xen_alloc_ptpage(struct mm_struct *mm, u32 pfn,
unsigned level)
make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
if (level == PT_PTE)
pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
- else if (level == PT_PMD)
- pin_pagetable_pfn(MMUEXT_PIN_L2_TABLE, pfn);
} else
/* make sure there are no stray mappings of
this page */
@@ -715,7 +713,8 @@ static void xen_release_ptpage(u32 pfn, unsigned level)
if (PagePinned(page)) {
if (!PageHighMem(page)) {
- pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
+ if (level == PT_PTE)
+ pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
}
}
--
1.5.4.5
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