linux-kernel - Re: [PATCH v2] dax: enable dax fault handler to report VM_FAULT

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Message-ID: <fe325e29-718c-20e3-c7fd-2b8b39e3d87e@oracle.com>
Date:   Tue, 18 Apr 2023 11:55:40 -0700
From:   Jane Chu <jane.chu@...cle.com>
To:     dan.j.williams@...el.com, vishal.l.verma@...el.com,
        dave.jiang@...el.com, ira.weiny@...el.com, willy@...radead.org,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] dax: enable dax fault handler to report
 VM_FAULT_HWPOISON

Ping, any comment?

thanks,
-jane

On 4/6/2023 4:01 PM, Jane Chu wrote:
> 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 <jane.chu@...cle.com>
> ---
>   drivers/nvdimm/pmem.c | 2 +-
>   fs/dax.c              | 2 +-
>   include/linux/mm.h    | 2 ++
>   3 files changed, 4 insertions(+), 2 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..c93191cd4802 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);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1f79667824eb..e4c974587659 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3217,6 +3217,8 @@ static inline vm_fault_t vmf_error(int err)
>   {
>   	if (err == -ENOMEM)
>   		return VM_FAULT_OOM;
> +	else if (err == -EHWPOISON)
> +		return VM_FAULT_HWPOISON;
>   	return VM_FAULT_SIGBUS;
>   }
>