On Tue, Aug 23, 2016 at 7:53 PM, Dan Williams <dan.j.willi...@intel.com> wrote:
> On Tue, Aug 23, 2016 at 6:29 PM, Kani, Toshimitsu <toshi.k...@hpe.com> wrote:
>>> On Tue, Aug 23, 2016 at 4:47 PM, Kani, Toshimitsu <toshi.k...@hpe.com>
>>> wrote:
>>> > On Tue, 2016-08-23 at 15:32 -0700, Dan Williams wrote:
>>> >> On Tue, Aug 23, 2016 at 11:43 AM, Toshi Kani <toshi.k...@hpe.com>
>>> >> wrote:
>>> > :
>>> >> I'm not sure about this fix. The point of honoring
>>> >> vmem_altmap_offset() is because a portion of the resource that is
>>> >> passed to devm_memremap_pages() also contains the metadata info
>>> block
>>> >> for the device. The offset says "use everything past this point for
>>> >> pages". This may work for avoiding a crash, but it may corrupt info
>>> >> block metadata in the process. Can you provide more information
>>> >> about the failing scenario to be sure that we are not triggering a
>>> >> fault on an address that is not meant to have a page mapping? I.e.
>>> >> what is the host physical address of the page that caused this fault,
>>> >> and is it valid?
>>> >
>>> > The fault address in question was the 2nd page of an NVDIMM range. I
>>> > assumed this fault address was valid and needed to be handled. Here is
>>> > some info about the base and patched cases. Let me know if you need
>>> > more info.
>>> >
>>> > Base
>>> > ====
>>> >
>>> > The following NVDIMM range was set to /dev/dax.
>>>
>>> With ndctl create-namespace or manually via sysfs? Specifically I'm
>>> looking for what the 'align' attribute was set to when the
>>> configuration was established. Can you provide a dump of the sysfs
>>> attributes for the /dev/dax parent device?
>>
>> I used the ndctl command below.
>> ndctl create-namespace -f -e namespace0.0 -m dax
>>
>> Here is additional info from my note for the base case.
>>
>> p {struct dev_pagemap} 0xffff88046d0453f0
>> $3 = {
>> altmap = 0xffff88046d045410,
>> res = 0xffff88046d0453a8,
>> ref = 0xffff88046d0452f0,
>> dev = 0xffff880464790410
>> }
>>
>> crash> p {struct vmem_altmap} 0xffff88046d045410
>> $6 = {
>> base_pfn = 0x480000,
>> reserve = 0x2, // PHYS_PFN(SZ_8K)
>> free = 0x101fe,
>> align = 0x1fe,
>> alloc = 0x10000
>> }
>
> Ah, so, on second look the 0x490200000 data offset looks correct. The
> total size of the address range is 16GB which equates to 256MB needed
> for struct page, plus 2MB more to re-align the data on the next 2MB
> boundary.
>
> The question now is why is the guest faulting on an access to an
> address less than 0x490200000?
Does the attached patch fix this for you?
From 506cdd2c4ec0f9283ac4eb92259f2e8a71c5b637 Mon Sep 17 00:00:00 2001
From: Dan Williams <dan.j.willi...@intel.com>
Date: Tue, 23 Aug 2016 19:59:31 -0700
Subject: [PATCH] dax: fix device-dax region base
The data offset for a dax region needs to account for an altmap
reservation in the resource range. Otherwise, device-dax is allowing
mappings directly into the memmap or device info-block area, with crash
signatures like the following:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
IP: [<ffffffff811ac851>] get_zone_device_page+0x11/0x30
Call Trace:
follow_devmap_pmd+0x298/0x2c0
follow_page_mask+0x275/0x530
__get_user_pages+0xe3/0x750
__gfn_to_pfn_memslot+0x1b2/0x450 [kvm]
? hrtimer_try_to_cancel+0x2c/0x120
? kvm_read_l1_tsc+0x55/0x60 [kvm]
try_async_pf+0x66/0x230 [kvm]
? kvm_host_page_size+0x90/0xa0 [kvm]
tdp_page_fault+0x130/0x280 [kvm]
kvm_mmu_page_fault+0x5f/0xf0 [kvm]
handle_ept_violation+0x94/0x180 [kvm_intel]
vmx_handle_exit+0x1d3/0x1440 [kvm_intel]
? atomic_switch_perf_msrs+0x6f/0xa0 [kvm_intel]
? vmx_vcpu_run+0x2d1/0x490 [kvm_intel]
kvm_arch_vcpu_ioctl_run+0x81d/0x16a0 [kvm]
? wake_up_q+0x44/0x80
kvm_vcpu_ioctl+0x33c/0x620 [kvm]
? __vfs_write+0x37/0x160
do_vfs_ioctl+0xa2/0x5d0
SyS_ioctl+0x79/0x90
entry_SYSCALL_64_fastpath+0x1a/0xa4
Cc: <sta...@vger.kernel.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Fixes: ab68f2622136 ("/dev/dax, pmem: direct access to persistent memory")
Reported-by: Abhilash Kumar Mulumudi <m.abhilash-ku...@hpe.com>
Reported-by: Toshi Kani <toshi.k...@hpe.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
drivers/dax/pmem.c | 2 ++
include/linux/memremap.h | 1 +
kernel/memremap.c | 9 +++++++++
3 files changed, 12 insertions(+)
diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
index dfb168568af1..0603637df162 100644
--- a/drivers/dax/pmem.c
+++ b/drivers/dax/pmem.c
@@ -116,6 +116,8 @@ static int dax_pmem_probe(struct device *dev)
if (rc)
return rc;
+ res.start += vmem_altmap_resource_offset(altmap);
+
nd_region = to_nd_region(dev->parent);
dax_region = alloc_dax_region(dev, nd_region->id, &res,
le32_to_cpu(pfn_sb->align), addr, PFN_DEV|PFN_MAP);
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 93416196ba64..7265b83cdbea 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -24,6 +24,7 @@ struct vmem_altmap {
};
unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
+resource_size_t vmem_altmap_resource_offset(struct vmem_altmap *altmap);
void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns);
#ifdef CONFIG_ZONE_DEVICE
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 251d16b4cb41..941e897c52a8 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -384,6 +384,15 @@ unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
return altmap->reserve + altmap->free;
}
+resource_size_t vmem_altmap_resource_offset(struct vmem_altmap *altmap)
+{
+ /* number of bytes from base where data starts after the memmap */
+ if (!altmap)
+ return 0;
+ return vmem_altmap_offset(altmap) * PAGE_SIZE;
+}
+EXPORT_SYMBOL_GPL(vmem_altmap_resource_offset);
+
void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns)
{
altmap->alloc -= nr_pfns;
--
2.5.5
