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Date:   Mon, 31 Oct 2022 15:10:16 -0500
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Subject: Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR
 allocation when SNP is enabled
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To:     Borislav Petkov <bp@alien8.de>, vbabka@suse.cz
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
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References: <cover.1655761627.git.ashish.kalra@amd.com>
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From:   "Kalra, Ashish" <ashish.kalra@amd.com>
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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.
>