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

[Kalra, Ashish]

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&data=05%7C01%7Cashish.kalra%40amd.com%7C7b2d39d6e2504a8f923608dac792224b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638041727879125176%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=KBJLKhPQP23vmvY%2FNnbjZs8wTJs%2FrF%2BiU54Sdc4Ldx4%3D&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