Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled

[Kalra, Ashish]

Just to add here, writing to any of these pages from the Host
will trigger a RMP #PF which will cause the RMP page fault handler
to send a SIGBUS to the current process, as this page is not owned
by Host.

So calling memory_failure() is proactively doing the same,
marking the page as poisoned and probably also killing the
current process.

Thanks,
Ashish

On 10/25/2022 5:25 AM, Borislav Petkov wrote:
> On Fri, Oct 14, 2022 at 03:00:09PM -0500, Kalra, Ashish wrote:
> > If it is "still" accessed/touched then it can cause RMP #PF.
> > On the other hand,
> >
> >   * PG_hwpoison... Accessing is
> >   * not safe since it may cause another machine check. Don't touch!
> >
> > That sounds exactly the state we want these page(s) to be in ?
> >
> > Another possibility is PG_error.
>
> Something like this:
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index e66f7aa3191d..baffa9c0dc30 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -186,6 +186,7 @@ enum pageflags {
>   	 * THP.
>   	 */
>   	PG_has_hwpoisoned = PG_error,
> +	PG_offlimits = PG_hwpoison,
>   #endif
>   
>   	/* non-lru isolated movable page */
>
> and SNP will have to depend on CONFIG_MEMORY_FAILURE.
>
> But I'd let mm folks correct me here on the details.