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

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Date:   Wed, 16 Nov 2022 04:28:11 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Vlastimil Babka <vbabka@...e.cz>
Cc:     Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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        "Kaplan, David" <David.Kaplan@....com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR
 allocation when SNP is enabled

On 11/15/2022 11:19 PM, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Tue, Nov 15, 2022 at 04:14:42PM +0100, Vlastimil Babka wrote:
>> Cc'ing memory failure folks, the beinning of this subthread is here:
>>
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F3a51840f6a80c87b39632dc728dbd9b5dd444cd7.1655761627.git.ashish.kalra%40amd.com%2F&amp;data=05%7C01%7Cashish.kalra%40amd.com%7C7b2d39d6e2504a8f923608dac792224b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638041727879125176%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=KBJLKhPQP23vmvY%2FNnbjZs8wTJs%2FrF%2BiU54Sdc4Ldx4%3D&amp;reserved=0
>>
>> On 11/15/22 00:36, Kalra, Ashish wrote:
>>> Hello Boris,
>>>
>>> On 11/2/2022 6:22 AM, Borislav Petkov wrote:
>>>> On Mon, Oct 31, 2022 at 04:58:38PM -0500, Kalra, Ashish wrote:
>>>>>        if (snp_lookup_rmpentry(pfn, &rmp_level)) {
>>>>>               do_sigbus(regs, error_code, address, VM_FAULT_SIGBUS);
>>>>>               return RMP_PF_RETRY;
>>>>
>>>> Does this issue some halfway understandable error message why the
>>>> process got killed?
>>>>
>>>>> Will look at adding our own recovery function for the same, but that will
>>>>> again mark the pages as poisoned, right ?
>>>>
>>>> Well, not poisoned but PG_offlimits or whatever the mm folks agree upon.
>>>> Semantically, it'll be handled the same way, ofc.
>>>
>>> Added a new PG_offlimits flag and a simple corresponding handler for it.
>>
>> One thing is, there's not enough page flags to be adding more (except
>> aliases for existing) for cases that can avoid it, but as Boris says, if
>> using alias to PG_hwpoison it depends what will become confused with the
>> actual hwpoison.
> 
> I agree with this. Just defining PG_offlimits as an alias of PG_hwpoison
> could break current hwpoison workload.  So if you finally decide to go
> forward in this direction, you may as well have some indicator to
> distinguish the new kind of leaked pages from hwpoisoned pages.
> 
> I don't remember exact thread, but I've read someone writing about similar
> kind of suggestion of using memory_failure() to make pages inaccessible in
> non-memory error usecase.  I feel that it could be possible to generalize
> memory_failure() as general-purpose page offlining (by renaming it with

But, doesn't memory_failure() also mark the pages as PG_hwpoison, and 
then using it for these leaked pages will again cause confusion with 
actual hwpoison ?

Thanks,
Ashish

> hard_offline_page() and making memory_failure() one of the user of it).
> 
> Thanks,
> Naoya Horiguchi
>