Messages in this thread | | | Date | Tue, 15 Nov 2022 12:15:52 -0600 | Subject | Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled | From | "Kalra, Ashish" <> |
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On 11/15/2022 11:24 AM, Kalra, Ashish wrote: > Hello Vlastimil, > > On 11/15/2022 9:14 AM, 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%7C944b59f239c541a52ac808dac71c2089%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638041220947600149%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=do9zzyMlAErkKx5rguqnL2GoG4lhsWHDI74zgwLWaZU%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. >> >>> But there is still added complexity of handling hugepages as part of >>> reclamation failures (both HugeTLB and transparent hugepages) and that >>> means calling more static functions in mm/memory_failure.c >>> >>> There is probably a more appropriate handler in mm/memory-failure.c: >>> >>> soft_offline_page() - this will mark the page as HWPoisoned and also has >>> handling for hugepages. And we can avoid adding a new page flag too. >>> >>> soft_offline_page - Soft offline a page. >>> Soft offline a page, by migration or invalidation, without killing >>> anything. >>> >>> So, this looks like a good option to call >>> soft_offline_page() instead of memory_failure() in case of >>> failure to transition the page back to HV/shared state via >>> SNP_RECLAIM_CMD >>> and/or RMPUPDATE instruction. >> >> So it's a bit unclear to me what exact situation we are handling here. >> The >> original patch here seems to me to be just leaking back pages that are >> unsafe for further use. soft_offline_page() seems to fit that scenario >> of a >> graceful leak before something is irrepairably corrupt and we page >> fault on it. >> But then in the thread you discus PF handling and killing. So what is the >> case here? If we detect this need to call snp_leak_pages() does it mean: >> >> a) nobody that could page fault at them (the guest?) is running >> anymore, we >> are tearing it down, we just can't reuse the pages further on the host > > The host can page fault on them, if anything on the host tries to write > to these pages. Host reads will return garbage data. > >> - seem like soft_offline_page() could work, but maybe we could just >> put the >> pages on some leaked lists without special page? The only thing that >> should >> matter is not to free the pages to the page allocator so they would be >> reused by something else. >> >> b) something can stil page fault at them (what?) - AFAIU can't be >> resolved >> without killing something, memory_failure() might limit the damage > > As i mentioned above, host writes will cause RMP violation page fault. >
And to add here, if its a guest private page, then the above fault cannot be resolved, so the faulting process is terminated.
Thanks, Ashish
> >>> >>>> >>>>> Still waiting for some/more feedback from mm folks on the same. >>>> >>>> Just send the patch and they'll give it. >>>> >>>> Thx. >>>> >>
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