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

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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.





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