Re: [PATCH v3] x86/fault: Send a SIGBUS to user process always for hwpoison page access.

[Andy Lutomirski]

> On Mar 1, 2021, at 11:02 AM, Luck, Tony <tony.luck@xxxxxxxxx> wrote:
> 
> 
>> 
>> Some programs may use read(2), write(2), etc as ways to check if
>> memory is valid without getting a signal.  They might not want
>> signals, which means that this feature might need to be configurable.
> 
> That sounds like an appalling hack. If users need such a mechanism
> we should create some better way to do that.
> 

Appalling hack or not, it works. So, if we’re going to send a signal to user code that looks like it originated from a bina fide architectural recoverable fault, it needs to be recoverable.  A load from a failed NVDIMM page is such a fault. A *kernel* load is not. So we need to distinguish it somehow.

> An aeon ago ACPI created the RASF table as a way for the OS to
> ask the platform to scan a block of physical memory using the patrol
> scrubber in the memory controller.  I never did anything with it in Linux
> because it was just too complex and didn't know of any use cases.
> 
> Users would want to check virtual addresses. Perhaps some new
> option MADV_CHECKFORPOISON to madvise(2) ?
> 
> -Tony