2023-04-06 17:58:37

by Jane Chu

Subject: [PATCH] dax: enable dax fault handler to report VM_FAULT_HWPOISON

When dax fault handler fails to provision the fault page due to
hwpoison, it returns VM_FAULT_SIGBUS which lead to a sigbus delivered
to userspace with .si_code BUS_ADRERR. Channel dax backend driver's
detection on hwpoison to the filesystem to provide the precise reason
for the fault.

Signed-off-by: Jane Chu <[email protected]>
---
drivers/nvdimm/pmem.c | 2 +-
fs/dax.c | 14 ++++++++++++--
2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index ceea55f621cc..46e094e56159 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -260,7 +260,7 @@ __weak long __pmem_direct_access(struct pmem_device *pmem, pgoff_t pgoff,
long actual_nr;

if (mode != DAX_RECOVERY_WRITE)
- return -EIO;
+ return -EHWPOISON;

/*
* Set the recovery stride is set to kernel page size because
diff --git a/fs/dax.c b/fs/dax.c
index 3e457a16c7d1..3f22686abc88 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1456,7 +1456,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,

map_len = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size),
DAX_ACCESS, &kaddr, NULL);
- if (map_len == -EIO && iov_iter_rw(iter) == WRITE) {
+ if (map_len == -EHWPOISON && iov_iter_rw(iter) == WRITE) {
map_len = dax_direct_access(dax_dev, pgoff,
PHYS_PFN(size), DAX_RECOVERY_WRITE,
&kaddr, NULL);
@@ -1550,11 +1550,21 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
}
EXPORT_SYMBOL_GPL(dax_iomap_rw);

+/*
+ * Concerning hwpoison triggered page fault: dax is THP, a pmd
+ * level fault handler will fallback (VM_FAULT_FALLBACK) before
+ * give up, hence return VM_FAULT_HWPOISON which implies
+ * corrupted range is PAGE_SIZE.
+ */
static vm_fault_t dax_fault_return(int error)
{
if (error == 0)
return VM_FAULT_NOPAGE;
- return vmf_error(error);
+ else if (error == -ENOMEM)
+ return VM_FAULT_OOM;
+ else if (error == -EHWPOISON)
+ return VM_FAULT_HWPOISON;
+ return VM_FAULT_SIGBUS;
}

/*
--
2.18.4

2023-04-06 19:39:15

by Matthew Wilcox

Subject: Re: [PATCH] dax: enable dax fault handler to report VM_FAULT_HWPOISON

On Thu, Apr 06, 2023 at 11:55:56AM -0600, Jane Chu wrote:
> static vm_fault_t dax_fault_return(int error)
> {
> if (error == 0)
> return VM_FAULT_NOPAGE;
> - return vmf_error(error);
> + else if (error == -ENOMEM)
> + return VM_FAULT_OOM;
> + else if (error == -EHWPOISON)
> + return VM_FAULT_HWPOISON;
> + return VM_FAULT_SIGBUS;
> }

Why would we want to handle it here instead of changing vmf_error()?

2023-04-06 20:43:09

by Jane Chu

Subject: Re: [PATCH] dax: enable dax fault handler to report VM_FAULT_HWPOISON

On 4/6/2023 12:32 PM, Matthew Wilcox wrote:
> On Thu, Apr 06, 2023 at 11:55:56AM -0600, Jane Chu wrote:
>> static vm_fault_t dax_fault_return(int error)
>> {
>> if (error == 0)
>> return VM_FAULT_NOPAGE;
>> - return vmf_error(error);
>> + else if (error == -ENOMEM)
>> + return VM_FAULT_OOM;
>> + else if (error == -EHWPOISON)
>> + return VM_FAULT_HWPOISON;
>> + return VM_FAULT_SIGBUS;
>> }
>
> Why would we want to handle it here instead of changing vmf_error()?

I think it's related to the comment about the the corrupted range of
a hwpoison caused fault - something no need to worry about now.

I will move the change to vmf_error() in a respin.

Thanks!
-jane