linux-kernel - [PATCH 4.9 83/88] device-dax: fix pmd/pte fault fallback handling

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Message-Id: <20170328122752.078005293@linuxfoundation.org>
Date:   Tue, 28 Mar 2017 14:31:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: [PATCH 4.9 83/88] device-dax: fix pmd/pte fault fallback handling

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Dave Jiang <dave.jiang@...el.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@...r.kernel.org>
Reported-by: Jeff Moyer <jmoyer@...hat.com>
Signed-off-by: Dave Jiang <dave.jiang@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -334,6 +334,7 @@ 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;
@@ -344,6 +345,9 @@ 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__,
@@ -389,6 +393,7 @@ 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;
@@ -405,6 +410,16 @@ 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) {