linux-kernel - RE: [PATCH v5 1/1] dax: enable dax fault handler to report VM_FAULT

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Date:   Sat, 24 Jun 2023 22:51:42 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jane Chu <jane.chu@...cle.com>, <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 v5 1/1] dax: enable dax fault handler to report
 VM_FAULT_HWPOISON

Jane Chu wrote:
> When multiple processes mmap() a dax file, then at some point,
> a process issues a 'load' and consumes a hwpoison, the process
> receives a SIGBUS with si_code = BUS_MCEERR_AR and with si_lsb
> set for the poison scope. Soon after, any other process issues
> a 'load' to the poisoned page (that is unmapped from the kernel
> side by memory_failure), it receives a SIGBUS with
> si_code = BUS_ADRERR and without valid si_lsb.
> 
> This is confusing to user, and is different from page fault due
> to poison in RAM memory, also some helpful information is lost.
> 
> Channel dax backend driver's poison detection to the filesystem
> such that instead of reporting VM_FAULT_SIGBUS, it could report
> VM_FAULT_HWPOISON.
> 
> If user level block IO syscalls fail due to poison, the errno will
> be converted to EIO to maintain block API consistency.
> 
> Signed-off-by: Jane Chu <jane.chu@...cle.com>

Reviewed-by: Dan Williams <dan.j.williams@...el.com>