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Subject[PATCH 4.10 105/111] device-dax: fix pmd/pte fault fallback handling
Date
4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Jiang <dave.jiang@intel.com>

commit 0134ed4fb9e78672ee9f7b18007114404c81e63f upstream.

Jeff Moyer reports:

With a device dax alignment of 4KB or 2MB, I get sigbus when running
the attached fio job file for the current kernel (4.11.0-rc1+). If
I specify an alignment of 1GB, it works.

I turned on debug output, and saw that it was failing in the huge
fault code.

dax dax1.0: dax_open
dax dax1.0: dax_mmap
dax dax1.0: dax_dev_huge_fault: fio: write (0x7f08f0a00000 -
dax dax1.0: __dax_dev_pud_fault: phys_to_pgoff(0xffffffffcf60
dax dax1.0: dax_release

fio config for reproduce:
[global]
ioengine=dev-dax
direct=0
filename=/dev/dax0.0
bs=2m

[write]
rw=write

[read]
stonewall
rw=read

The driver fails to fallback when taking a fault that is larger than
the device alignment, or handling a larger fault when a smaller
mapping is already established. While we could support larger
mappings for a device with a smaller alignment, that change is
too large for the immediate fix. The simplest change is to force
fallback until the fault size matches the alignment.

Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
Cc: <stable@vger.kernel.org>
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/dax/dax.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -427,6 +427,7 @@ static int __dax_dev_fault(struct dax_de
int rc = VM_FAULT_SIGBUS;
phys_addr_t phys;
pfn_t pfn;
+ unsigned int fault_size = PAGE_SIZE;

if (check_vma(dax_dev, vma, __func__))
return VM_FAULT_SIGBUS;
@@ -437,6 +438,9 @@ static int __dax_dev_fault(struct dax_de
return VM_FAULT_SIGBUS;
}

+ if (fault_size != dax_region->align)
+ return VM_FAULT_SIGBUS;
+
phys = pgoff_to_phys(dax_dev, vmf->pgoff, PAGE_SIZE);
if (phys == -1) {
dev_dbg(dev, "%s: phys_to_pgoff(%#lx) failed\n", __func__,
@@ -482,6 +486,7 @@ static int __dax_dev_pmd_fault(struct da
phys_addr_t phys;
pgoff_t pgoff;
pfn_t pfn;
+ unsigned int fault_size = PMD_SIZE;

if (check_vma(dax_dev, vma, __func__))
return VM_FAULT_SIGBUS;
@@ -498,6 +503,16 @@ static int __dax_dev_pmd_fault(struct da
return VM_FAULT_SIGBUS;
}

+ if (fault_size < dax_region->align)
+ return VM_FAULT_SIGBUS;
+ else if (fault_size > dax_region->align)
+ return VM_FAULT_FALLBACK;
+
+ /* if we are outside of the VMA */
+ if (pmd_addr < vma->vm_start ||
+ (pmd_addr + PMD_SIZE) > vma->vm_end)
+ return VM_FAULT_SIGBUS;
+
pgoff = linear_page_index(vma, pmd_addr);
phys = pgoff_to_phys(dax_dev, pgoff, PMD_SIZE);
if (phys == -1) {

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