On Fri, Jul 13, 2018 at 1:52 AM, Naoya Horiguchi
<n-horiguchi@xxxxxxxxxxxxx> wrote:
> On Wed, Jul 04, 2018 at 02:41:06PM -0700, Dan Williams wrote:
>> mce: Uncorrected hardware memory error in user-access at af34214200
>> {1}[Hardware Error]: It has been corrected by h/w and requires no further action
>> mce: [Hardware Error]: Machine check events logged
>> {1}[Hardware Error]: event severity: corrected
>> Memory failure: 0xaf34214: reserved kernel page still referenced by 1 users
>> [..]
>> Memory failure: 0xaf34214: recovery action for reserved kernel page: Failed
>> mce: Memory error not recovered
>>
>> In contrast to typical memory, dev_pagemap pages may be dax mapped. With
>> dax there is no possibility to map in another page dynamically since dax
>> establishes 1:1 physical address to file offset associations. Also
>> dev_pagemap pages associated with NVDIMM / persistent memory devices can
>> internal remap/repair addresses with poison. While memory_failure()
>> assumes that it can discard typical poisoned pages and keep them
>> unmapped indefinitely, dev_pagemap pages may be returned to service
>> after the error is cleared.
>>
>> Teach memory_failure() to detect and handle MEMORY_DEVICE_HOST
>> dev_pagemap pages that have poison consumed by userspace. Mark the
>> memory as UC instead of unmapping it completely to allow ongoing access
>> via the device driver (nd_pmem). Later, nd_pmem will grow support for
>> marking the page back to WB when the error is cleared.
>
> By the way, what happens if madvise(MADV_SOFT_OFFLINE) is called on
> a dev_pagemap page? I'm not sure that cmci can be triggered on the
> nvdimm device, but this injection interface is open for such a case.
> Maybe simply ignoring the event is an expected behavior?
Yeah, I should explicitly block attempts to MADV_SOFT_OFFLINE a
dev_pagemap page because they are never onlined. They'll never appear
on an lru and never be available via the page allocator.
>
> A few comments/quetions below ...
>
>>
>> Cc: Jan Kara <jack@xxxxxxx>
>> Cc: Christoph Hellwig <hch@xxxxxx>
>> Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
>> Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
>> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>> ---
>> include/linux/mm.h | 1
>> mm/memory-failure.c | 124 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 123 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index a0fbb9ffe380..374e5e9284f7 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2725,6 +2725,7 @@ enum mf_action_page_type {
>> MF_MSG_TRUNCATED_LRU,
>> MF_MSG_BUDDY,
>> MF_MSG_BUDDY_2ND,
>> + MF_MSG_DAX,
>> MF_MSG_UNKNOWN,
>> };
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 4d70753af59c..161aa1b70212 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -55,6 +55,7 @@
>> #include <linux/hugetlb.h>
>> #include <linux/memory_hotplug.h>
>> #include <linux/mm_inline.h>
>> +#include <linux/memremap.h>
>> #include <linux/kfifo.h>
>> #include <linux/ratelimit.h>
>> #include "internal.h"
>> @@ -263,6 +264,39 @@ void shake_page(struct page *p, int access)
>> }
>> EXPORT_SYMBOL_GPL(shake_page);
>>
>> +static unsigned long mapping_size(struct page *page, struct vm_area_struct *vma)
>> +{
>> + unsigned long address = vma_address(page, vma);
>> + pgd_t *pgd;
>> + p4d_t *p4d;
>> + pud_t *pud;
>> + pmd_t *pmd;
>> + pte_t *pte;
>> +
>> + pgd = pgd_offset(vma->vm_mm, address);
>> + if (!pgd_present(*pgd))
>> + return 0;
>> + p4d = p4d_offset(pgd, address);
>> + if (!p4d_present(*p4d))
>> + return 0;
>> + pud = pud_offset(p4d, address);
>> + if (!pud_present(*pud))
>> + return 0;
>> + if (pud_devmap(*pud))
>> + return PUD_SIZE;
>> + pmd = pmd_offset(pud, address);
>> + if (!pmd_present(*pmd))
>> + return 0;
>> + if (pmd_devmap(*pmd))
>> + return PMD_SIZE;
>> + pte = pte_offset_map(pmd, address);
>> + if (!pte_present(*pte))
>> + return 0;
>> + if (pte_devmap(*pte))
>> + return PAGE_SIZE;
>> + return 0;
>> +}
>> +
>
> The function name looks generic, but this function seems to focus on
> devmap thing, so could you include the word 'devmap' in the name?
Ok.
>
>> /*
>> * Failure handling: if we can't find or can't kill a process there's
>> * not much we can do. We just print a message and ignore otherwise.
>> @@ -292,7 +326,10 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
>> }
>> tk->addr = page_address_in_vma(p, vma);
>> tk->addr_valid = 1;
>> - tk->size_shift = compound_order(compound_head(p)) + PAGE_SHIFT;
>> + if (is_zone_device_page(p))
>> + tk->size_shift = ilog2(mapping_size(p, vma));
>> + else
>> + tk->size_shift = compound_order(compound_head(p)) + PAGE_SHIFT;
>>
>> /*
>> * In theory we don't have to kill when the page was
>> @@ -300,7 +337,7 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
>> * likely very rare kill anyways just out of paranoia, but use
>> * a SIGKILL because the error is not contained anymore.
>> */
>> - if (tk->addr == -EFAULT) {
>> + if (tk->addr == -EFAULT || tk->size_shift == 0) {
>> pr_info("Memory failure: Unable to find user space address %lx in %s\n",
>> page_to_pfn(p), tsk->comm);
>> tk->addr_valid = 0;
>> @@ -514,6 +551,7 @@ static const char * const action_page_types[] = {
>> [MF_MSG_TRUNCATED_LRU] = "already truncated LRU page",
>> [MF_MSG_BUDDY] = "free buddy page",
>> [MF_MSG_BUDDY_2ND] = "free buddy page (2nd try)",
>> + [MF_MSG_DAX] = "dax page",
>> [MF_MSG_UNKNOWN] = "unknown page",
>> };
>>
>> @@ -1111,6 +1149,83 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>> return res;
>> }
>>
>> +static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>> + struct dev_pagemap *pgmap)
>> +{
>> + struct page *page = pfn_to_page(pfn);
>> + const bool unmap_success = true;
>> + unsigned long size = 0;
>> + struct to_kill *tk;
>> + LIST_HEAD(tokill);
>> + int rc = -EBUSY;
>> + loff_t start;
>> +
>> + /*
>> + * Prevent the inode from being freed while we are interrogating
>> + * the address_space, typically this would be handled by
>> + * lock_page(), but dax pages do not use the page lock. This
>> + * also prevents changes to the mapping of this pfn until
>> + * poison signaling is complete.
>> + */
>> + if (!dax_lock_mapping_entry(page))
>> + goto out;
>> +
>> + if (hwpoison_filter(page)) {
>> + rc = 0;
>> + goto unlock;
>> + }
>> +
>> + switch (pgmap->type) {
>> + case MEMORY_DEVICE_PRIVATE:
>> + case MEMORY_DEVICE_PUBLIC:
>> + /*
>> + * TODO: Handle HMM pages which may need coordination
>> + * with device-side memory.
>> + */
>> + goto unlock;
>> + default:
>> + break;
>> + }
>> +
>> + /*
>> + * Use this flag as an indication that the dax page has been
>> + * remapped UC to prevent speculative consumption of poison.
>> + */
>> + SetPageHWPoison(page);
>
> The number of hwpoison pages is maintained by num_poisoned_pages,
> so you can call num_poisoned_pages_inc()?
I don't think we want these pages accounted in num_poisoned_pages().
We have the badblocks infrastructure in libnvdimm to track how many
errors and where they are located, and since they can be repaired via
driver actions I think we should track them separately.
> Related to this, I'm interested in whether/how unpoison_page() works
> on a hwpoisoned dev_pagemap page.
unpoison_page() is only triggered via freeing pages to the page
allocator, and that never happens for dev_pagemap / ZONE_DEVICE pages.
